What the "clipboard" on a MacBook Pro, and how to delete a snapshot from it? Also, can you install iBooks onto the MacBook Pro and if so, how?

Hello Everyone,

I was wondering if anyone can explain what the "Clipboard" is and how to delete a snapshot of the screen from it. I found the Clipboard on my MacBook Pro under Finder, then Edit, and then clicking on Show Clipboard. It does show a picture or snapshot of the screen I took and that's all. I'd like to delete that. Can anyone tell me what the Clipboard is and how to delete that screenshot? Also, is there any way to put iBooks onto the MAC? Thanks in advance for any and all help!!!!