GTKRadiant mapping problems

[Plasma]

I have installed GtkRadiant but when i go to make a map or follow tutorials they have all their special texture menus and their structures have shapes and size. I cant find any shaders or textures on mine and when i put down a structure, no matter what it is, it is a cube about 10 game units across.  plz tell me where i can get these things and how i can get textures