TTRPGs are adults playing pretend with the structure of a game to give it shape. Some TTRPGs have more rules and the resultant playing pretend is heavily structured, some TTRPGs have fewer rules and the resultant playing pretend is as freeform as when kids do it. I think the rules and the gamelike structure help to launder the roleplaying aspect past all of your cultural conditioning that tells you that such a thing is childish and that you shouldn't do it, so you could see them as a way to get in touch with your creativity with a group of similarly-minded people in a setting where fewer people will judge you or think you're cringe for expressing yourself honestly.

Anyway the way you do it is you gather a group of people and decide on a game, then arrange a regular meeting time (this is by far the hardest part). Once you're sitting down at a table together (or on the same VOIP call) the actual game mechanics are decided by what you're playing. Most commonly TTRPGs take the form of pulpy fantasy action where a rag tag group of heroes save the world - this gives each player the opportunity to express themselves through their character and a common goal to work towards in the game mechanics - but there's so many RPGs out there you can find a game for just about any genre of storytelling you can imagine.