Two Rooks and a King vs a King
This is a very simple mate. You don't have to use your king at all, which makes it double easy. The object is to drive the king to one of the four edges of the board. One rook is used to stop the king from backtracking while the other delivers the checks to push the king to the side. If the King attacks you. Move away. It is a common sense mate.

One Rook and A King vs a King
This mate is a bit uncomfortable as your opponents king can get slippery and prove hard to sheperd. For these types of mates an understanding of The Opposition is needed. The opposition is just the fact that since a king cannot move inside the attacking range of another king it must move away. You use your rook to stop your opponents king from moving away from the corner your pushing him/her towards. The object of the mate is to get your opponents king into one the corners. The mate looks like this.
 --- --- ---
|   |WK |   |
 --- --- ---
|   |   |   |
 --- --- ---
|WR |   |BK |
 --- --- ---

Here is the notation of a typical One rookmate. White King is on e4 with the white rook on f3. The black king is on g2. Notice the way that the King and rook move in order to push the black king.

1. Ke3 Kg1
2. Rf2 Kh1
3. Kf3 Kg1
4. Kg3 Kh1
5. Rf1++

That's how it's done.

Endgames in Chess
Chess Openings