Quote: "I don't think you need to do any of this. I certainly didn't."
Quote: "You don't, just download it in steam and you're ready to go.
At least this is the legal way."
That's only for Steam Re-Distributed mods such as Dystopia.
However Steam doesn't adopt all the modifications found out there, nor do all the modifications out their have their own installers...
Other than that, if they don't have a installer and the files in the ZIP/RAR/Compressed format etc, need installing manually.
@Oolites post,
Legal way? Their aint even a Illegal way of installing mods for the
Original steam to use, lol
Quote: "It comes with instructions and there are entire wikis on the subject."
Only if the developers are smart enough to include a *.txt... Unlike many others, but you are right...

"Your greatest teacher is your harshest critic"-'Butterfingers'