Foreword

In Islam, prayer is the most important act of worship. It is the pillar of religion, as it has been narrated in the  hadith. Also, it has been related from the Prophet (p) that, "It is the first of man’s deeds that is considered. If it is deemed in order, the rest of his actions shall be examined. If not, the rest of his deeds can no longer be considered". "Its similitude is that of a flowing river. So long as you wash five times a day in this river, you achieve thorough cleanliness. The same goes for prayer; whenever you perform a prayer, you rest assured that your sins that fall between prayers shall be forgiven", said the Prophet (s.a.w.).
Mu’awiyah bin Wahab asked Imam As-Sadiq (a.s. )about the best of deeds, that is best loved by Allah, which could bring man closest to his Lord. He said, "I do not know of any thing, apart from knowledge, more meritorious than prayer. Do not you see that the good servant of Allah, Jesus son of Mary (a.s. )said,...and He has enjoined on me prayer and poor-rate so long as I live(13/91)". 
Our Imam, Abu Abdullah As-Sadiq (a.s ) took very seriously the task of urging people to keep up prayer. When Abu Basir was led in to Um Hamidah, the Imam’s wife to pay his respects on the Imam’s death, it was reported that both cried. Afterwards she was quoted as saying, "O Father of Mohammad, I wished you were there when Abu Abdullah was in the throws of death. It was an amazing scene; he opened his eyes and asked for all our kin to be gathered together; she added that we did so. He looked at them and said, "Our intercession is not going to be granted to any one who takes prayer lightly.

Types of Obligatory Prayer
1. Prayer is divided into two categories. Obligatory and voluntary. The obligatory ones are six:
a. The five daily prayers. These are subh, dhuhr, asr, maghrib, and isha’.
b. Tawaf prayer.
c. Ayat (signs) prayer.
d. Prayer for the souls of the dead. Please refer to para. (129) of the Chapter on Rules Concerning the Dead.
e. Prayer, on qadha’ basis, of the eldest son for his dead father, as will be discussed in some detail.
f. Prayers of the two Eids( al-Fitr and al-Adhha), only if it be held by the Imam or a just ruler representing him.
Practically, though, it could be said that, at the time of the occultation of Imam Al-Mahdi  (a.s.), the prayers of the two Eids are not obligatory, for lack of requirements. However, the obligatory prayers are those mentioned in a to e .The rest are voluntary and mustahab. They do not become wajib except by any of the general Wajib reasons, such as nadhr or oath.

The Format of Prayer                                      
2. The maximum number of ruka’a’ in compulsory prayers is four, as in isha’; the minimum is two, as in subh. As for voluntary prayers, the minimum is one ruka’a, which is that of witr )an odd number of ruka’a’).
However, ruka’a is one of the main units of a prayer; the only exception is the prayer for the dead as it comprises a number of takbirs not ruka’a.
The first ruka’a of every prayer, apart from Ayat prayer and the two Eids prayers can be carried out thus:
After niyyah, the worshipper should start with takbiratul ihram, i.e. by saying Allahu Akbar. Once that said, you are truly in prayer.
Recitation of suratul Fatihah, followed by another surah comes next.
After that comes bowing, i.e. by placing one’s hands on one’s knees and uttering Subhana Rabiyal Adheemi wa Bihamdih - Glory be to my Lord, the Great, and praise belongs to Him.
Going back to an upright standing position.
Assuming a posture of sujood, by placing one’s hands, knees, and toes on the prayer mat; as for the forehead it should be placed on something earthly, wood, or paper.
While in this position, you should say )Subhana Rabiyal Al ’ala wa Bihamdih - Glory be to my Exalted Lord, and praise belongs to Him.
Raising the forehead and going back to a kneeling position to be followed by another sujood.
Should the prayer be that of one ruka’a, the worshipper should, while still in a kneeling position say the following, Ashhadu Anla Illah Illal Lah, Wahdahu La Sharika Lah, Wa Ashhadu Anna Mohammadan Abduhu Wa Rasuluh, Allahumma Salli Ala Mohammadin Wa Aali Mohammad- I bear witness that there is no god apart from Allah, Who is unique and without partners. I also bear witness that Muhammad is His servant and Messenger. O God! Bless Mohammad and the progeny of Muhammad. This is called tashahhud.
Then Tasleem, i.e. Assalamu Alaikum Wa Rahmatul Lahi Wa Barakatuh - May peace be upon you all, and Allah’s Mercy and blessing- should be said. This is the shortened format of tasleem.Tasleem concludes the prayer.
Should the prayer consist of two ruka’a, such as that of subh, the worshipper should go back to a standing position before tashahhud and tasleem and repeat what they have done in the first ruka’a, apart from takbiratul ihram.
Upon lifting the forehead from sujood, they should assume a sitting upright position and say both tashahhud and tasleem, thus concluding prayer.
In a three-raka’a prayer, like that of maghrib, the worshipper should confine themselves to saying tashahhud at the end of the second ruka’a and go back to an upright standing position and say :Subhanal Lahi Wal Hamdu Lillahi, Wala Illaha Illal Lahu, Wallahu Akbar - Glory be to Allah, and praise be to Allah, there is no god but Allah, and Allah is greater. This is called dhikr. They should then go a bowing position followed by the two sujoods, and back to the upright sitting position to say tashahhud and tasleem.
In a four-raka’a prayer, such as that of dhuhr, no tashahhud or tasleem should be said at the end of the third ruka’a. Instead, the worshipper should go back to the upright standing posture to repeat the routine of the third ruka’a, then perform the two sujoods, tashahhud and tasleem.
Among the mustahab acts in prayer is qunoot )the raising of both hands for supplication( in the second ruka’a after reciting al-fatihah and a second surah, but before bowing. This could be done in a two, three, or four-raka’a prayers.
Accordingly, ruka’a’, the two sujoods, and the utterances during ruku and sujood are fixed parts in every main unit )ruka’a’( of prayer. Takbiratul ihram is part and parcel of the first ruka’a’, tashahhud and tasleem are parts of the last ruka’a, recitation ]of the two surahs are integral parts of the first and second ruka’a’. Dhikr is part of the ruka’a’ that comes after the second one. If prayer is not going to be concluded in the second ruka’a, it takes an extra part, i.e. tashahhud after the second sujood has been performed.
3. So the most important parts of prayer are the following:
a. Takbiratul Ihram.
b. Recitation.
c. Ruku )bowing).
d. Sujood )prostration). 
e. Dhikr 
f. Tashahhud.
g. Tasleem.
4. In addition to the aforesaid parts, there are other requirements that should be fulfilled. These are of two kinds. The worshipper should fulfill the first category, while the second category has to do with prayer itself.
General guidelines for the worshipper:
a. The person should be tahir and has performed wudhu.
b. Their body and clothes must be tahir.
c. Their private parts should be covered.
d. Clothes worn during prayer should not be made of parts of a dead animal or that whose flesh is not sanctioned for human consumption. Male worshippers should not be wearing gold or silk. As for carrying parts of the dead body of an animal, an inherently najis thing, or that which has become najis, it does not invalidate prayer. Wearing clothes whose material could be suspect, i.e. whether the animal was slaughtered according to Islamic practice, is allowed.
It is more likely however that there is no harm in carrying, in prayer, anything that belongs to an animal whose flesh is not fit for human consumption. Yet, it is strongly recommended, as a matter of ihtiyat, that one has to shy away from it.
e. Facing the qiblah, i.e. the direction where the Holy Ka’ba is situated, in prayer.
f. The intention behind offering the prayer should be that of seeking closeness to Allah, the Exalted.  
g. When praying, the worshipper should designate the name of that particular prayer. For example, when praying subh, making niyyah to say it should be with the exclusive objective of achieving nearness to Allah.
As for the general requirements of prayer itself, they are as follows:
a. Adherence to the order of parts/units that comprise prayer, in that takbiratul ihram should come before recitation, and the latter before ruku, and so on.
b. Succession of the acts of prayer should be observed, in that there must not be a break or a long pause between its parts.
c. Placing the forehead during sujood on the earth, a piece of wood, a paper, or the like, as will be discussed.
This is a skeleton run on prayer and how it should be conducted within the prescribed conditions.
There are though other parts and special requirements where some prayers differ from the others. The prayer of the two Eids, for example, consists of additional takbirs. The daily prayers have to be performed on their appointed time. However, we shall be discussing the following:
a. Outline all types of prayer and how to conduct each one of them.
b. Outline the general guidelines, and parts, of prayer and discuss briefly the rules governing each one of them.
c. Outline the general rules of prayer in the form of: 
1. Things that invalidate prayer,
2. Saying prayer by way of qadha’, 
3. Shortcomings in prayer, 
4. Doubt in prayer, 
5. Congregational prayer, 
6. The differences between obligatory and voluntary prayers.