How do you make your own templates?

Maybe this is an obvious question but I would love to make templates in the future. Is there a software for this?
I’ve made a few simple things just by drawing it out on pencil and paper but those are really simple things like certain letters and punctuation but I’ve never made something more complicated.
Having done some FPP now I understand the concept that you basically have to start with the most inner piece and work your way out.