where to start (in my POV) in summary:
well, for starter, you need to understand the theory first, such as, what is a tcode, standard or custom object, program, etc.
From there, move on to the technical part, such as creating or modifying table data, syntax, program, etc.
This is just a little part of it, but you could search for tutorial in the internet or this forum as many had discussed about it.
