Sorry for not responding earlier I somehow missed your previous post.
You can either join the rooms or host your own.
You start on a spaceship (though there are other maps, but Skeld is most played one) together with usually 10 players. Depending on game mode, either 1 or 2 or 3 of you are impostor, but you don’t know that because all of you look identical.
The only way to discover the impostor is either witnessing a murder or suspicious behavior. But the thing is, you have to convince people and sometimes they might not believe you. If you are not an imposter, you have a set of tasks that you need to do among other things. If you and your crews complete the task, you win even if you haven’t discovered the impostor.
Now as for impostor, your objective is to kill the crew or sabotage the ship without being discovered.
It requires thinking and planning if you don’t want to be discovered easily.
As with any games, some players are just bad at this game. Finding the room with the group of good players is best experience.
And also, there is chat.

It’s a whole another story, sometimes it’s just hilarious. When someone report the body or calls an emergency meeting, players discuss via chat. It is wonderful place.