*sigh*
Once again I had one of those dunkoph moments where I missed all these topics.
To make designs like mine, I just use the photoshop brush tools, to make some paint splash-like effects.
If you want to make planets or explosions or things like that, I suggest finding tutorials on the internet.
But, I use photoshop. I don't know if you do, so using google could be helpful for tutorials.
But, here's how to split an avatar from it's background:
Step 1:

Get a picture you want to split the background from.
Step 2:

Select the wand tool
3:

Select an area that you want to be removed.
4:

Press 'delete' to get rid of that area. (Note - the checks mean a transparent area)
5:

Repeat until done.