To level up, gain exp by posting blogs, skins, texture packs, and many other submissions, etc. etc.
Commenting, getting comments, and getting subscribers (who are like subscribers on Youtube or people who follow you on Twitter) are good ways of gaining exp.
To skin, simply download either of the programs Paint.net or MCSkin3D. They are my favorite skinning programs. In Paint.net, drag the Char file from the Minecraft Bin into the drawing space, and you're ready to use any tools to paint the skin. Then upload the file onto Planet Minecraft.
In MCSkin3D, you don't need to upload anything. Just click on the New Skin button in the menu on the left. You'll figure it out. MCSkin3D is my choice of program!
Hope this helped!
