A BPS file is a patch containing (for instance) a hack. By patching this file to an unmodified ROM image of SMW, you will get the hack which lies in the BPS patch.
Why use patches instead of ROMs?
Because giving away commercial ROM files is illegal. The patch contains only the differences between the full hack and the original ROM. This way, hacks can be given away legally.
How do I use a patch?
Use Floating IPS to apply a BPS patch to a clean ROM of the game that it is a hack of. Some emulators also let you play a hack without patching if the ROM name and the patch name are the same and are in the same directory.
How do I create a BPS patch?
Also with Floating IPS, you can select "Create Patch" and choose the clean ROM first, then the hack, then name your new BPS file.
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