They should usually just have to be put in the materials folder, but look at the .vmt of any of them and put them in the folder path it says in there.

K. Heres a link to a tut i made for custom textures: Custom Map Textures

Now. Just to answer your questions, you can open up the .vmt with a text editor (like notepad), or with the VTFEdit (in the tutorial theres a link).

You must specify the location of each .vtf (the actual image) in the .vmt (the text file, because all hammer does is look for the .vmt

Example of a .vmt file


If you've placed the textures into the wrong spot, then it will come up as purple and black checkers in Hammer. So read the tut, and you should understand how to do it better.