Just create a brand new folder dedicated to FiveM/FiveReborn on your desktop, then stick FiveM or FiveReborn related files into the folder.
Wanna run maps? Use the usermaps folder, which you also need to create and fill with some maps. We have a few maps here that are FiveReborn/FiveM optimized that you can use, keep in mind, these maps will forever be deserted. No traffic, no people, nothing. Just you.
Installing car mods is different too, but I cannot remember where they go. I hoped I helped anyway, though.