A few people have mentioned how they have noticed me using shortcut keys when I am using my computer, or when I am fixing something on theirs, and have asked me what they are. Well, some of the common Mac OS shortcut keys can be found and even modified in system preferences, under Keyboard & Mouse, on the Keyboard Shortcuts tab.
There are a lot of useful commands to be found there, and just in case you wanted a list, Apple provides one here. Ever want to quickly shut down, restart, or log off of your machine, check this one too.