Textures vs. Bases?

Hello, everyone! I'm new to the whole icon-making thing. I've been poking through some tutorials and such, just getting ideas and getting started. I'm seeing a lot of "paste this texture" or "paste this base", which brings me around to the point of this post, and my question: what is the difference between bases and textures? When should one use a texture instead of a base, and vice versa? I've been clicking through the FAQs and the tutorials, but I can't seem to find an explanation of the two anywhere. Also, I'm using PSP7, so anyone who can give me specifics to using bases and textures with that program will get many brownie points. :)

Thank you /so/ much in advance for any replies!