When my son was about three years old, I started teaching him to learn the letters. I went to a stationary store and bought all the letters of the alphabet plus the ones that are always together, th..oo..ee..etc. They came in several sizes so I got about 4 inch ones, laid them out on 1 inch pine boards and cut them out. Sanded and let him 'help' paint them with wild colors. When he went on to first grade i gave them to the kindergarten teacher and she was thrilled at having them for her class. She saw how much they helped him learn.
Stationary stores or teacher stores will give a solid template.
I made the letters from fabric (very large for little ones to toss around ) for the older two girls when they were about one year old. Both loved them and learned what each letter was quickly.