First it gives you a code like A1B2C3 ect, this is referring to the row and column of the letter. It is a little weird in that it only goes up to 5 and then starts the next row, I would use a picture to describe it but I don't have easy access to the prompt.
So for an example, A1 is the first letter first row, A2 is the second letter first row, A6 is the first letter on the second row, B1 is the first letter on the third row...ect...