Hi Harv, I've had several MRIs.
The MRI machine is like a tube with a bed that goes into it. You're laid on the bed, rest your head on a bracket to make sure your head doesn't move and it brings you back into the (large!) tube. They give you some earbuds to help block out the noise of the machine, which kind of sounds like a brick in a washing machine!
It doesn't hurt at all, but it's a bit intimidating. I had to take out all of my piercings (hard when you have so many...) and my shoes and was in there for quite a while, so they asked me to bring some of my own music on a USB key. The NHS did a great write-up about it that you can find here.
There's actually a cute little mobile VR app to help explain it to kids. It's very comprehensive and will give you a much better idea of how it works than my ropey explanation!
Have a look here.
I hope it goes well for you. We always see 'scan' and panic, but I've had three in my time and they're nothing to be worried about.