How do I make a ROM Hack?

[WaterPhish]

Ok, I have Visual Boy Advance, and thats pretty much it. I don't know how to load ROMs in or how to export them to my 3ds. Can anybody help?

 

[FAST6191]

You are asking many things there and I am not entirely sure what you are heading for.

VBA is a GBA (and GB/GBC) emulator, there are some versions with decent debugging tools as well that older hackers might have used (no$gba debug version and mgba / https://wrongbaud.github.io/posts/ghidra-debugger/ being what most would probably go for these days if looking for a hacking GBA emulator/debugger).

https://gbatemp.net/threads/gbatemp-rom-hacking-documentation-project-new-2016-edition-out.73394/ is my guide to GBA and DS ROM hacking if you wanted that. Some also like https://www.romhacking.net/start/ .

"export them to my 3ds"
Whatever way you normally play GBA games on your 3ds should work for ROM hacks as well -- outside of a handful of what are considered bugs in the hack it is not like the NES or SNES where you get oddities that make certain emulators on embedded devices cry. Not sure what we are suggesting for this one these days but whatever current guide to it you find to playing GBA games should do for this as well.

Most hacks are distributed as patches (smaller, legally less tricky, gives options for other things). IPS was still very common but its failings became apparent so you might encounter UPS, bsdiff, xdelta (which has various versions), beat and a few others. Read the readme it comes with, and you can usually find patchers on https://www.romhacking.net/utilities/ or indeed https://www.romhacking.net/patch/ for an online patcher. The GBA does not really have any header issues like you might have for the NES and SNES, or ROM variations like the megadrive bin/smd/whatever stuff, to that end your main problems are likely to be if the patch is for another region, a different version (sometimes bugfixes happened), or maybe the patch wants a scene release (sometimes the people dumping the games would add extra intros and trainers) and you have to force it on the clean version or vice versa, plus whatever is necessary to get saves from emulator to flash cart/3ds emulator and back again if you happen to have a save you want to keep.