Welcome Marina.
This is probably one of the best places for what you are asking for. The community is friendly and helpful and there are diverse views on how to do things (so don't worry if you are told things that contradict the way you think things should work, YMMV, as they say, and some people play differently).
Play by Post (PbP) is a bit of a different beast to playing games live, the feedback loop is much slower and it can take a long time to get things done. But that slowness can also be a boon: You can take your time to look things up, or to ask around, and don't have to have answers at your fingertips. All GMs eventually learn that they can not 'know all the rules', and resort to going with what seems to work best in the moment and looking up the actual rule after the game. That can still happen with PbP, but is less common due to more time.
As
bowl mentioned,
GM Mentoring Project can be a valuable resource. Don't hesitate to ask any questions you have.
There are lots of games happening here, all the time, so you can get a chance to try playing a variety. If you want to try GMing a few, make it clear you are new and want
helpful players and I am sure you will find many willing to help and support your effort.
With the constant reading of RPG books, I assume you are not only interested in fantasy games? What else interests you? You can mention specific game rulesets if you know them, or genres of books, movies or TV to give a general idea.
