To use these boards, you will need a variety of different fonts for each letter. You can find these online. I print out the letters with all of the fonts on 5 different colors of paper (this will help at a center to not get letters mixed up with other students at the table). This will help students realize that they may see different ways to make letters in different fonts.
For example: a's, J's, I's, etc., can be different when using different fonts.
I usually stick to mixing 3-4 letters - too may letters can be overwhelming. When you are ready to move to a new letter board, students LOVE to help sort the letters back into the bags :)