i'm not a pro so don't hate. here's a simple explanation of the typewriter.

if you're starting from the right, here's what you do:
1) concentrate on a pull up toward your right hand
2) with your right arm bent and left arm straight, push over to the left side (here you would use your right tricep to push from the right and your left bicep to pull to the left)
3) do a negative by slowly letting your (now bent) left arm downward in a controlled fashion
4) the same method applies when if you want to start pulling from the left

do bicycles to activate abdominal muscles, but keeping your knee up while doing a typewriter will have more of an effect

do an Lsit (legs lifted 80-90 degrees) typewriter for a full core strengthening workout

Good luck and happy training !