This thread probably belongs in General Discussion rather than the Support section, but I'll answer your question.
Currently, there's not much use for freighters aside from hauling around the stuff you loot from battle, but that's not to say there never will be a good use for them. The campaign in its current state is basically a placeholder. It is planned that things like trade and industry will be viable, but the focus for most of the development so far has been on the combat, fleshing it out and making it feel good. Almost nothing pertaining to trade or industry is implemented into the base game just yet, however. (I don't actually know what mods do with that stuff, so someone else might provide better information)
So, there's not much use for freighters now, but the intent is that they will be more useful in future updates.
Oh, and there's no real use for fuel just yet either, other than being something to sell. As I mentioned, the campaign is just a placeholder and there's only one system to fly around.
