First of all I copied the lines of an existing modpack in installed packs file and changed the names and made a custom folder named the same as what I called it in the file. When I did it, there wasn't any modpack with that name, so never knew it would link it automaticly. It's not that hard to make tbh.
You just need to be sure you make the lines you add in the installed packs file right and that you have the right version for mods.