Ruy Lopez

I do not understand why it is so great
---> A simplist explanation : white's second and third moves put pressure on black's e5 pawn, and force black to react from the very beginning
Can someone please explain to me how to use it correctly and how to play against it?
---> it is a very complex opening, would take a book to give just basic info

Diakonia has made very good posts in two of your three recent threads on almost exactly the same topic.
Have you replied to those posts? No.
Have you replied to any of the 14 posts on those threads? No.
I won't repeat what he's said. If you want to improve then you should follow the advice already given to you. If you keep posting these threads you may even be removed from the site for spamming. Probably not though, I'm not that lucky...