Ok I want to make low poly models for an RTS game. I am not a great modeler, but I can make something in the shape of a tank, and make it look all right from the iso view. My problem is figuring out how I can texture my tank, building or character. I have seen some textures before where it is all the parts of say a tank, but they are all mixed up. Or like a human. There will be a face, then a foot next to it, then a torso, then another foot, then some arms, then a leg etc. How do you do that?

What you are describing is called unwrapping. Usually in 3d games it's recommended to use fewer maps on your models, so the uv's are condensed. Check out your 3d application's help about unwrapping, see some examples and tutorials :)