In case you are confused about what is the Command key on an Apple Mac, here's where it is:
There are two Command keys on a standard Apple Mac keyboard. If you've learned to touch-type, use the right one when you type letters on the left-hand side of the keyboard, and vice versa. If you don't touch-type and you are a right-hander, use the key on the left. If you are a left-hander and don't touch-type, use the key on the right.