Welcome, Jack. As the others said above, turn up before 20:00 UTC so you have a chance to say hallo and get the game and Mod versions checked. It also lets the Duty Officer realize you are available to assign to a crew. Do not worry about choosing a crew. While you are a cadet you will be assigned to various crews so that you have a chance to try different stations and ships and gain a sense of what the crews are like. You can put in a request for a specific ship after that.
Be aware that promptly at 20:00 UTC we will move to a specific teamspeak channel representing the briefing room and we will take a rollcall and receive a briefing in the plan for the session.
If you would like to get a handle on the roleplay and what happens in the missions, take a look in the Forums under Personal Logs.