Putting Models & Materials into Garry's Mod

Hey, i have Half Life 2 Episode 1 & 2 on my PC, but there both in my Program files.

How can i get the models & materials, maps e.t.c into Garry’s Mod? (Also in Program files)

Please help.

Start Gmod, select Gmod Options from the main menu and mount the games.

And how will i find the difference? So if i get the Antlion guardian, it will work?

Yes.