Filing taxes on artist commissions

I am a young artist (self-employed) who is nearing $400 in earnings (when I would have to file for taxes), and I have absolutely no idea where to start in reporting my earnings for the next year. I've read and read on the IRS site, but none of it makes sense. 

I want to know what forms to file and how to file them. All of my earnings are on the PayPal website.