You need to know:
-(ofc base scripting)
-what is menu is and how dvars are working
-what is scriptmenuresponse and fetching it in script (_menus.gsc)
-how to save/read from file

Thats all what you need! If you positively meet the above conditions, then I'll you can create your own account system.
Open IzNo's files and check them out (how does the script/menu is built).