Ivan.
I think you are either going to love play by post or hate it.
This is so much different from video play. You get to use your imagination to create a character with feelings and depth. Video games are reaction and eye-hand skills to react and if things go bad you just start over. In these games there are no do overs! You build on what has happened but you can't go back and try again. And your character can get killed. There are some worlds where a character might be raised and brought back, but not in all games. It those cases you may be able to create a new character, but it is different.
Think of this as writing a fantasy adventure novel as a gruop.
There are some rules in different games set to help guide you as what and how your character can do things. You get to live through this character and express thier feelings and ideas. I find copies of rule set to help me understand the world in which I will be playing. That said I am not a rules lawyer and I don't memorize everything.(Just ask the DMs I play for.)
As for the game and the DM. There are prewritten game stories with goals to achive available that help shape the game, but as character act and react the game never plays the same twice.
There are also some DMs that write their own stories and create whole worlds to play in. They present a situation and your character and the other respond. Now working together helps, so use of the Q&A section to talk to each other is a good idea.
I enjoy trying to write a good story as much as succeeding in the action I try.
Now speaking to that, you only get to say what your character is trying to do and how they are trying to do it in story form. The DM rolls the dice to measure your success and then writes the result in story form. It just keep going that way.
If you pick a game and read it from the start you will see more about what I am trying say.
So, your choice, play someone elses precanned video game or live the life of your character in your mind and in the story.
Hope you enjoy this game style.
Ody