They will weigh you, take your measurements,and your height! Ask you some questions, what d'you want to gain out of the gym, just toning or losing weight etc. Ask about your health and any problems you have and whether or not you do any exercise. You must be totally honest, it's easier in the end to admit you're a wannabe ex couch potato than have them think you're semi fit and give you harder work lol.
The will then introduce you to the gym. I did 3 minutes on the treadmil ( thought I was going to die!),3 minutes on the xtrainer (nearly had to call the paramedics!),3 minutes on the bike. Then was told when I came for a workout they would be 10 minutes each! Well that caused a stand up row lol! ( I survived lol I now do 30 mins on the xtrainer etc!). Then we went around the main equipment where I was shown how to do them and at what weights and repetitions! It's all written down on your workout card with seat heights and positions etc. They will show you where to put your card etc.
It's nothing too drastic, and they're very helpful so if you forget anything or need advice just ask, that's what they're their for!
Most trainers enjoy their job and if you give them 100% or at least are seen to be trying your best they will give you a 100%
At my gym all of the trainers are fantastic but my own 2 personal sadists are brilliant, they know I like to moan and whinge, which they just ignore as they also know I like to be pushed!
It's nothing scary, so just enjoy it, it can end up being great fun!
I never thought I'd be a bit of a gym bunny at my size and weight, but here I am a size 22/24 from a size 28/30 and I love it!
Good luck and have fun.