Any tips for a new iMac user?

I am a longtime Windows user.
My wife has an iMac, which I occasionally use, but I don’t pretend to understand it.
We just bought a new iMac as a gift to each other for Christmas.
I have struggled to get it set-up, and this far.
For example, I was sure the mouse was faulty, because it didn’t have a visible red light. Finally realized it normally doesn’t.
Any tips?