I go a fair bit. If you’re a newbie then you need to book a taster session. If there’s enough of you , you can book a group taster session with just your mates and a trainer but it might cost more than you think. Just try and get a taster session with all of you at once but phone and ask for best results, expect a long waiting list.
They rent shoes and helmets and bikes. Take gloves, your own helmet, riding clothes and changing/washing things if you want. They have a tap by the track but take a water bottle anyway.
IIRC with about 12 people it cost about 25 quid each for a couple of hours with a trainer. You’ll not be bumping into anyone special. I must have been 30 times now and never seen anyone famous.
Depending on the trainer, you may well get to do a 1 lap solo sprint, maybe even a bit of a race but that depends on how confident the trainer is with you and how good the people with you are. If it’s all fat mountain bikers who can’t hold a cadance or a line or who don’t understand fixed bikes, it’s unlikely you’ll do more than ride round in circles.
It gets warm, very warm. Take a towel and spare clothes.