Try command and "", the key that's usually just left of "1" and has "" and "~" on it. That's the default. You can change it to whatever you want: System Preferences -> Keyboard -> Shortcuts -> Keyboard -> Move focus to next window.
I'm also relatively new to a Mac, just one year since switching teams after many years. It's different. I still miss being able to start a separate process by clicking the icon in the dock. Or creating a text file with a right click.