What to expect at an assessment day

Hello, new to here so sorry if this is in the wrong place.

The RAC contacted me last week about a job I applied for and I'm going to an assessment centre on Tuesday...

I was just wondering if anyone could tell me what to expect? I don't normally get nervous, but this time I am. Think that is probably because I've always worked in independent garages, so never really had a suit and tie assessment day/interview

Thank you :)