We Muslims have been commanded by Allah to offer essential (Fardh) prayers (Namaz – Salah) five times a day. (Unfortunately many of us now-a-days do not take it seriously). These five essential prayers are offered at fixed times. Fajr ( before dawn), Zohar (after mid-day, just after noon), Asr (starts in the beginning of evening and remains till sunset), Maghrib (just after sunset) and Isha, (after one and a quarter hour after sunset, remains till before dawn). These five salah are preferably offered in congregation in the mosque. These may be offered individually, but bear lesser reward than offered in congregation.
There is a special fardh prayer which is offered on every Friday. It is offered only in the congregation. There are two other special prayers, that is Namaz Eid al fitr and Eid al Adha. These are offered in congregation only by men (women may also join in congregation, but in separate hall, they can offer these two salah at home individually, bearing the same award as for men in congregation). Men can not offer these three salah Juma (Friday) salah, Eid al Fitr and Eid al Adha individually at home.
PS: I'll try to elaborate briefly the value of prayer at a later time.