TF2 not working in GMOD

I dont know why Gmod cant find and read TF 2 models , maps , items. I have Team Fortress 2 and I have Gmod. I really dont understand why MY GMOD cant find these TF2 things.
Please help.

Have you tried mounting the files?

Go to GMOD Settings and tick Team Fortress 2.
Click OK and restart garrys mod.