While there is only one cleric class, each cleric may choose to worship a different deity. This must be chosen during character creation. All clerics endeavor to increase the influence of their deity in the world of Derlith. Because of the ways of worship, each deity has their own restrictions, which should all be listed below.
All clerics are able to pray to their deity in order to get an increase in piety.
For a more insight on the healing abilities for each deity (since they all differ to some degree), the healing page has some helpful information.