OS X: Capture a piece of screen

This days I'm just testing my new macbook pro and I found the way to take a screenshot from just a piece of screen.

Here is the chain codes for this utility:

Cmd+MAY+3. Complete screen to a Desktop png
Cmd+Ctrl+MAY+3. Complete screen ready for paste.
Cmd+MAY+4. You can select a piece of your screen by a cursor, and save it automaticaly on the desktop.
Cmd+Ctrl+MAY+4. You can select a piece of your screen by a cursor and save it where you want.
Cmd+MAY+4 and the spacebar The cursor becomes a camera and you can select the aplication for create your 'appShot' saveing it automatically on the desktop.

Cmd+Ctrl+MAY+4 and the spacebar the same but ready for paste.