What To Do
The core of the game's day-to-day involves roleplay in the city of . When you first log into the game, you might want to introduce yourself on the game's channels. See help channel for syntax, but public Hello! is a good start.
You can find some roleplay in Sanctuary. You could ask on channels or use the where command to find other characters and go to join them.
If you want to have your character do something beyond the scope provided by roleplay in Sanctuary, then you have two main options. You can ask for an event to be run, if someone has time to do it. You can use the action system, which allows your character to attempt anything you want to try with them. Unless the scope of an event or action is really rather small, expect them to be set up to encourage the involvement of multiple players.
If you aren't sure how to proceed, you can always ask, either on channels or by request - see help request.