Flash n00b with questions

Can someone please tell me what exactly “getBounds” does? I’ve been reading about it and I don’t understand. I learned about it from this line of code:

if (_root.walls.hitTest(getBounds(_root).xMax, _y, true)) {

(The rest of the if statement isn’t important)

Also, can someone tell me how to add cheats to games? For example, if I want the game to spit out an extra life when you type “extralife”, what would I do?

Thanks!