GarageBand shortcuts not working

I'm working in Garageband 10.1 on a brand new MacBook Pro. I've tried using some of the shortcuts listed in the online manual, but every time I do, I get a brief flash on my screen, which I understand to be an error message saying "unknown keystroke". Particularly, I'd love to be able to use Control+Delete, as I'm trying to record audiobooks, and edit out mistakes. Are there preferences that need to be set in a specific way? Help please!