Follower
A follower is an individual who has accepted Religion into their life and chosen to align themselves with one of the four gods. In doing so they accept some minimal restrictions in return for their gods blessing.
The blessing is specific to each god and achieved when you have acquired twenty faith which you do through praying. The benefit is passive so you need take no special actions for it to be active. There are also minimal restrictions and the blessing and restrictions can be examined under each god's page, one each for Fo, Libila, Magranon, Vynora.
To become a follower you can either make a pilgrimage to the White Light or the Black Light on the wild server, or ask an appropriate priest or follower to convert you to their faith. The last option is available on both Wild and Freedom.
Once you've converted to a god your alignment can then change. Again read the page for your god to see what actions are relevant, being confessed or preached at by a priest will also help better your alignment.
Once you have reached thirty faith you can then, if you chose to, become a priest yourself with all the restrictions and benefits that ensue. To achieve this on Wild requires a pilgrimage to the either the White Light or the Black Light. On freedom a priest with forty faith or higher can raise you from follower to priest status.