There are 64 squares on the chessboard. 32 light and 32 dark.
Squares that run up and down the board vertically are lettered a through h.
There are 8 files on the chessboard.
Squares that run side to side or horizontally are called ranks. They are numbered 1 through 8. There are 8 ranks on the chessboard.
Diagonals are squares that run to opposite corners.