As awesome as Snapz Pro is, i'd feel remiss to not mention that there are some things lacking in this tutorial, particularly in the mention of the built-in screenshot functionality with the finder. I am constantly unimpressed with how little homework goes into articles like this.
Command + Control + Shift + 4 = selection tool, that puts the selection on your clipboard. If you go to a program like Mail, you can paste into mail. It creates a file as an attatchment. Guess what format it's in? Tiff.
Command + Control + Shift + 3 = puts the entire screen on your clipboard.
Command + Control + Shift + 4 then tap the spacebar = brings up a camera icon. Move it around the screen and it will highlight windows, icons, menus, etc. Click and whatever it highlighted will be put onto your clipboard. If you remove the "Control" from this key combo, it will create a PDF of it on your desktop.