Oh okay. If you tried twitter with twidere it's a bit the same thing.
I'll try to find you a "get started guide".
Basically you can
1) see "public" messages posted by people on the local timeline (lesbiab.space only) and the federated timeline (other instances of mastodon, pleroma, etc... connected to lesbiab.space) or see the messages of people you follow on your home timeline.
If you're on the web interface, see the menu top left
2) You can follow, be followed by, block and mute people. If you don't want to be followed by anybody, you can set your account to "private" in the settings : people who ask to follow you will appear in the "follow resquests" in the "get started menu" (you can access it by clicking on the three lines in the top left menu) ans you can accept or deny them. By default you accept anyone automatically