It is obligatory upon every Muslim individual to perform prayers in congregation (i.e. in the Masjid), except for a legal acceptable excuse such as sickness, cold weather or far distance.
The least number that should be present in order to perform a valid congregation prayer is two persons. That is, two persons are the least number that can form a congregation.
As for women, it is viewed permissible for them to attend the congregational prayer in mosques after taking the permission of their husbands. This is to be done on certain conditions; namely, women must not be perfumed nor should they show their adornment and they should perform prayer with a complete cover. Moreover, women are not to mingle with men and they must perform prayer while standing behind the rows of men.
It is obligatory upon the one who is led in prayer to fully follow the Imam (one who leads people in the prayer). He should not move before the Imam or delayed.
It is recommended for the Imam to recite aloud in the two Rak’ahs of Fajr Prayer, and in the first two Rak’ahs of Maghrib and ‘Ishaa’ Prayers.
One who is led in prayers is not obliged to recite Al-Faatihah in the Rak‘ahs in which the Imam recites loudly. However, if the prayer is to be performed secretly, or in the case that the one led in prayer does not hear the Imam, then he has to recite Al-Faatihah.
The one coming late for the congregational prayer is not to be regarded as having caught up with the prayer unless he prays at least one Rak‘ah (unit of prayer) thereof i.e. joining Imam in the sufficient bowing. So if the latecomer to congregational prayer reaches the prayer while the Imam is in the bowing position, he must pronounce the opening Takbeer (in prayer) while standing, then he should bow with the Imam preferably after a second Takbeer (saying Allahu Akbar). When one doubts catching up bowing, then if he is quite certain that he caught it, then such Rak‘ah is sufficient for him. But if not (he is uncertain that he caught bowing), he has to perform another Rak‘ah and perform the prostration of forgetfulness before Tasleem.
If the latecomer to congregational prayer gets the Imam in any position (in prayer), then he should follow him. when the Imam pronounces the second Tasleem (the final Salaams in prayer), the latecomer is to stand erect to perform whatever he has missed, yet he is not to stand before the second Tasleem pronounced by the Imam. The beginning of the prayer of the latecomer to congregational prayer is the part he catches up with Imam, and what he performs after the Tasleem (of the Imam) is the last part of it.
The one who is most entitled to lead the prayer is the one who has most knowledge of the Book of Allaah, then the one who has most of Fiqh, then by the one who migrated (made Hijrah) first; if they are equal in terms of recitation of Quran, Fiqh and Hijrah, then by the one who became Muslim first, then the elder one of them
It should be mentioned that congregacional prayers are obligatory for healthy Muslim men, and for women the best prayer is at home, due to her responsibilities with her children and home, and her delicate fragile nature. (Translator)