It's quite easy. You don't need any programming knowledge. Just buy a simple program for game making, a perfect program for a geometry dash clone. To figure out code and other stuff, YouTube/Internet has the answer.
Click to play:
geometry dash l b612 l retrica
The only basic skill you need is knowing how to use a computer. Its more of an 8-bit program so Crossy road would be a bit more complicated. I've never heard of Retry. I hope this helps. Good luck.