How do I make the 3 key combo for getting 3 levels of pic?
___________

Not exactly sure what you mean by 3 levels of pics but I think you mean being able to select multiple items at once. 2 methods:

Hold down the command key to select multiple items by clicking on each one.
or
Hold down the shift key to select a range of items.

This works throughout the Operating system. Select multiple pictures, emails, documents, etc…