This might have been better to put in the
Museum instead of the Museum shop. But first is you need to have a program ie Paint tool Sai, photoshop, gimp, etc in order to draw and do other stuff. There's a sticky somewhere talking about more art programs so yeah. Some are free some aren't, whichever fits your style basically.
I'm not sure what you mean by download a chibi, like a template or base to draw on and color over? If so then, you would need to credit the original artist and ask for permission to use those first if they are not free for use. Then just be creative and start experimenting?