The Monastery is a sort of Prayer Guild, but there isn't any requirements for the first level. There is, however, a 32 Prayer Requirment for anyone wishing to go to the top floor.
 Ground Level
The ground level contains nothing for higher levels, but is a great area for low levels. With several level 5 Monks (That will also heal you if you get low on health) and some cabbages (That you could also heal on), its a great place to train both Combat skills and Prayer.
 First (Top) Floor
The first floor of the Monastery has some other points of interest for both free members and members alike.
The first thing I'd like to mention: You need 32 Prayer to enter this level of the Guild. If you do not have 32 Prayer, kill some monks and bury the bones they drop. Or go to the Prayer Page for more information.
The second thing that you might want to know about is the Monk Robes on the east side of the top floor. These are useful if you're praying against a monster, but, however, they provide little or no protection against attacks if you are not praying. Use them wisely...
Another thing you might want to know is that theres one of the three Kharid Scorpions in the southeastern corner of the top floor. This is used for the Scorpion Catcher Quest
There is also an altar there. When prayed at, it fills your prayer points up like any other altar would, but it also adds 2 MORE prayer points! (For example, if you had 50 prayer, you would have 52/50 prayer when you use this altar) The only other altar that does this is the Nature Spirit altar.