Making a theme GPL?

I made up a wordpress theme for the forum software xenforo and I’m giving it away pretty much, it’s a free theme.

People have asked me what is the licence.

“It’s a free theme” is my reply.

“But what is the licence”.

What is the licence? how much does it matter to someone like me, just giving the thing away. Any info that is not 500 pages of legal documentation would be handy, the point of the GPL and what I must do as far as my theme goes. I compressed my js files? is this some type of encryption according to GPL? I have no idea. Is this licence required for wordpress HQ to acknowledge it even exists?
It sounds cool to have legal documents with a theme (shell script = search warrant), but what is the purpose if it’s free to begin with?