Also worth remembering is that every command that deletes really cuts. Which is to say, deletion commands like x and dd store the deleted content in the register that will be used when you hit p or P. This is important to know both because it can be very useful sometimes and because it can get in your way other times (e.g., if you're trying to repeat an action and keep replacing a line with another line, you'll have to paste before you delete so you don't override your register).