Step #3 Determining the best move

Chess is a game of war. Your objective is to overwhelm the opponents' king, but that shouldn't be your target every move. To know which of your pieces to move, you have to ask yourself a series of simple questions. We'll talk about the first one today: Can the opponent check or checkmate me right now if it was his/her turn?
This question right here will hopefully save you from that surprise checkmate. Evaluate the opponent's position, and don't underestimate them. Even if they are 7 years old, they're playing with the same pieces you are. Look closely for some of the simpler mates. If it's early in the game, watch your King's Bishop's pawn for threats against it. Learn the quick mates, and beware of them. Mark Lowery has an index of checkmating patterns you should learn to identify. Review these until you know them. They may even win you some games early on.
If the answer to this first question is yes, then answer the threat. Do what you can to stop the mating attack. If you have multiple ways to stop the threat, choose the way that will re-threaten the opponent to make them back off.

Step #2 - Stop Hanging Your Pieces

Soon after you learn to play chess, you have your first hurdle to overcome. You'll probably 'hang' your pieces. This means that you'll leave your pieces hanging out in the open with no defense. Before you move for your turn, review each and every one of your pieces (including pawns) to see if the opponent can take them for free or for cheap.
Let's say you have two pieces that can be taken by the opponent.

A knight that can be taken by their queen but the queen can be retaken by another piece

A pawn that can be taken by their bishop, but you cannot retake the bishop.

In this case, trading a knight for a queen is fine - focus instead on the free pawn. Games are won by your opponent racking up advantages on you, even one point at a time.
By now, you should know the relative values of the pieces...
1 - pawn
3 - knight, bishop (worth about the same depending on the board position)
5 - rook
9 - queen
infinite - king

Step #1 - Learn the Rules

Of course, there are numerous ways to do this. You could play online, check out web pages such as The Illustrated Rules of Chess and the more complete, but not quite so illustrated F.I.D.E. Laws of Chess. There are plenty of places to play online and each locale will have its own level of play. Playing at Pogo will give you chances to win money and to play other beginners.