Pawns are the most numerous (and usually smallest in physical size) piece in chess. Each player gets 8 and at the start of each game they take up the entire second row. Think of pawns as the initial shield to thwart advances and the first line to make your attack. Each side has more pawns than any other piece, but unfortunately the pawn is the weakest in the game. Generally, a pawn can move forward one space. This rule is only different in two instances. The first time each pawn is moved from its opening spot, you can choose to advance it either one space forward or two spaces forward. Once it has moved from this spot, the pawn must follow the one space ahead rule. The only other time a pawn can move differently is if it is in a spot to capture another piece. A pawn can capture a piece only one diagonal spot in front of it. Therefore, each pawn has two squares that it can capture. If an enemy piece moves to the spot diagonally to the left-front or right-front of your pawn, you can move to that spot and remove the enemy piece from the board. Pawns can never move backward.
Rooks
Most likely your rooks appear as castles. These two pieces are placed on the extreme outsides of the back row. Excluding the king, who is invaluable, the rook is considered the second most powerful weapon in your arsenal. A rook is able to move either horizontally or vertically and can do so for as many spaces as you like. If you want to move your rook from one corner of the board to the other and the lane is open, you can do it. Unlike the pawn, a rook captures another piece in the same way in which it moves. If an enemy piece is ahead of your rook vertically or horizontally, you can move your rook to that spot and remove the enemy piece from the board.