I started several years ago with Poser 1 (bald little plastic people) and I'm still learning new things! As Kelderek suggests, look through Freestuff (link at top of page) for a couple basic textures, see if you can apply them properly, then take a look at them in Photoshop or PSP to see how they works. Then experiment by making changes - it's trivial to use Hue-Saturation controls to change a texture. Beware that very high-resolution textures may tax your system too much, especially if you are using multiple high polygon count figures, hair and clothes. Start simple, don't worry about being able to do everything at first, and have fun.