KING vs KING, ROOK
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It doesn't really matter what you do when you're white. Black will force mate anyway.
Lost cause. Just so you know.
king v bishop - draw
king v 2 bishops - wins i believe
k v knight or two knights - draw
k v rook or queen - won
anything with pawns all depends on the situation
king v two bishops wins
king v knight and bishop wins but it's hard to do
Thank you everyone, it's helped. I must now concede defeat to my girl friend. She'll only win this one time I promise. Hah
Theoretically, black can force a checkmate against white. It's not even terribly difficult. But many beginners aren't good enough to do so. If you're white and you're not sure if black is a good enough players to force the win, just try to keep your king away from the edge of the board and count to 50 moves, in the hopes of a draw.
--Fromper
you best resign, but since your a beginner, you may aswell play on to see how to mate using king and rook. At some stage you will be the one with the black pieces! 
This is one idea of how the game might end. Some of the moves are imperfect, but there's nothing white can do to prevent checkmate as long as black has some idea of what he's doing.
I invite any corrections to errors I've made here.
King vs two Knights:
While it should be a draw, it is important for the weaker side to remember to never step on a corner square(a1, a8, h1, h8). Mate is possible, it just can't be forced.
Rag0r wrote: Thank you everyone, it's helped. I must now concede defeat to my girl friend. She'll only win this one time I promise. Hah
In the locker room:
"So my girlfriend beat me in a 100 yard dash the other day..."
"You can't even outrun a girl? Loser!"
At the chess club:
"So my girlfriend checkmated me the other day..."
"Whoa, your girlfriend is cool! Can we meet her?"
Don't complain, fella. 
HowDoesTheHorseMove wrote: Rag0r wrote: Thank you everyone, it's helped. I must now concede defeat to my girl friend. She'll only win this one time I promise. Hah
In the locker room:
"So my girlfriend beat me in a 100 yard dash the other day..."
"You can't even outrun a girl? Loser!"
At the chess club:
"So my girlfriend checkmated me the other day..."
"Whoa, your girlfriend is cool! Can we meet her?"
Don't complain, fella.
Thank you for the advice in this and your previous posting.
The correct checkmate for Black in this situation is to attempt to use his king to pin your king on the either Rows 1/8 or Files A/H and then use his rook to put you in check+checkmate. If your opponent knows the theory behind this endgame, and plays correctly, you will be checkmated regardless or what you do. If he does not know the theory behind this endgame, then you must attempt to avoid behind forced to the forementioned rows or files.
You donot have any other option but to resign.
I always tell my students to pick a direction and stick with it! 4. Re5+ isn't really necessary. It works here because it controls the center, but could be confusing if it's not used properly. Better, I think, is 4. Re1, holding the e file and threatening Rd1 if the white king doesn't move back onto the d file. It's complicated to try to do it by squeezing a file here and a rank there. It's easier for beginners to "see it" if they only work for one or the other. Since the given variation ends in forced mate, there's really no way I can say it's worse than what I teach my students to do, but I still think it's harder to grasp...
HowDoesTheHorseMove wrote: Rag0r wrote: Thank you everyone, it's helped. I must now concede defeat to my girl friend. She'll only win this one time I promise. Hah
In the locker room:
"So my girlfriend beat me in a 100 yard dash the other day..."
"You can't even outrun a girl? Loser!"
At the chess club:
"So my girlfriend checkmated me the other day..."
"Whoa, your girlfriend is cool! Can we meet her?"
Don't complain, fella.
And that's why I love chess players
Well, in case you made ~40 moves without moving a pawn or capturing a piece, you should waste time. If it's only ~30 moves, you can see if your girlfriend knows the rook mating pattern. If it's ~20 or less moves, you're hopeless-anyone can figure out the elementary mate in ~20 moves.
Black win
May be draw
Mariajoffil wrote:
May be draw
It was totally worth resurrecting a 16 year old dead thread for this great insight.
Or maybe not.
I know this is probably very elementary, but if I'm white, what should I do in this situation?