Forge Tools is a pretty broad name for "bunch of stuff you can use to mod". In the archive is map maker, a particle maker, developer executable (lets you spawn ships/buildings on the fly and such).
The only thing you need for yours, though, is trusty ole Notepad for the GameInfo files (in the Reference Data folder in the archive). And the tutorial pdf that goes over how to set up the mod and all that good stuff 
If you haven't extracted the archive yet, you can use something like WinRAR or 7zip to do it, and then you'll see all the stuff I'm talking about 