How do i add garrys mod textures, materials to my Source Sdk? (2014)

[Gesaffelstein]

I have problems with my Source Sdk! I have NO textures and I have NO materials for my garrys mod source sdk! Someone please help me I made Garrys mod and stuff onto it but I just cant make anything because I got no textures for my floors or walls that I will make if I figure out my problem. So if you know exactly what to do reply to this message so I can make a deathrun map if I am able to make it. So if you replyed thank you and ill just sit back and wait for a reply. hope it wont take long. ._.