All ladder letters are formed by starting at the top of the letter and then moving straight down. Some ladder letters start in the sky and are taller letters eg l and t. We call letters that start in the sky and are tall ascenders. Some ladder letters fall beneath the line and have a tail eg j and y. We call letters that fall below the line descenders. 

One armed robot letters are formed by starting at the top of the letter and then bouncing back up to retrace the line and then over. Some one armed robot letters are taller and start in the sky eg b h k. These letters are ascenders. Some one armed robot letters fall below the line eg p. This letter is a descender. 

Curly caterpillar letters start at the top of the letter and usually all start by forming the letter c first with exception of e, f and s. Curly caterpillars curl around. Some have ascenders as they are tall and go up to the sky eg d and f. Some have descenders and go below the line eg f, g and q. 

Zigzag monster letters all start at the top of the letter and have a diagonal zigzag lines. 

https://www.youtube.com/watch?v=PItRNtLlkcA

Please see the video link for examples and tutorials for letter formation