Cheat Sheet: https://gist.github.com/ur4ltz/d0167120a9fe718bdc048a2599ba139d
Important one is Meta+D. This opens dmenu, which lets you run commands, such as to open apps.
Dmenu isn’t my favorite. I like to download Fuzzel, an app launcher. It lists all your apps for you. I bind that to something Meta+A. Fuzzel also has a command running mode that operates like dmenu, which I bind to Meta+D.