looking for websites that teach this

[PrairieDuck]

I had noticed that some of my friends on other sites,make their own avatars and signatures together,which are called sets. I asked them how they learned to do that,and they told me they just tinker around on their comps. They also said that I could do some tinkering around myself,but I don't know where to start. Does anyone know of any helpful tutorial websites that could guide me to make my own?

I would also like to learn how to make my own computer wallpaper too.