Can someone help me how to make a category for select screen ?

[OldGamer]

for example a category menu for the select screen
I have no clue how they work or how its made 

I just need someone explain to me in baby step for easy understand on how to make this work
I know how to code and understand the system.def layout I just need someone tell me how its work in general and show me some trick method
on how all work and general.

Please don't tell me to use other people stuff... as example..
is best to just tell me in your level of knowledge
here an example