The crux of this hack relies on old 3DS firmware, specifically firmware revisions 4.1 to 4.5. Those firmware numbers are at least nine months out of date, but if your 3DS does have the older software, breaking its region lock is as simple as installing a special, patched launcher on a flash cartridge compatible with your 3DS' firmware revision. Once you open the launcher, the 3DS will be modified to accept games from other regions, though as Tiny Cartridge notes, there are issues when attempting to play certain games online due to their reliance on "game patches from region-specific eShops."
Keep in mind, this hack will not allow a user to play pirated games on his or her 3DS. Altering the firmware in this way only removes the handheld's region lock. You'll still need to import a legitimate 3DS cartridge from another territory to enjoy the system. Further, if you install this exploit, then attempt to update your 3DS using the standard firmware update method, the exploit will be deleted. There is a workaround offered for this issue in the hack's instructions, though it's slightly more complex than installing the hack by itself. If you opt to break your 3DS' region lock, we recommend paying very careful attention to the procedures outlined on the GBATemp forums.