Let's say you want to create a ball made out of leather. (Very original, isn't it ?).
1. Create a ball in a 3D program.
Note : the ball appears grey because there isn't any texture on it.2. Take an image of leather and "stick" it on the ball.
Note : This image is called texture.Without any texture, everything would look grey. If you have Vice City, inside you'll find the texture of Tommy Vercetti. His face looks flat, and so are all his clothes. In fact, by sticking this image on the 3D body, you'll have your Vercetti !
To illustrate, here are some images. The first one shows where the textures are going to be sticked. The second one is the texture itself, and the third shows Tommy in-game, for you to see where which texture was applied.