I still don't know much about the headers... What do they do?
If you want to play online, you need to assign each ROM a header. SKY3DS has public headers (dumped from a cart passed around a long time ago) that will get you banned when you go online. A private header assigned to each ROM makes it so that you have a unique online ID for that ROM (even if you use the same private header for every ROM). Hence allowing you to play games online.
Where it gets confusing is making sure you chose the right cartridge type (there's three manufacturers of 3DS cartridges) for the ROM. If you don't choose the right one, you'll get an error trying to get online.








