Affiliate Marketing Secrets

In 2012 I made $18,000 in self employment income. I am young and have only had 1 real job outside of my home. I was laid off from my last job and needed income fast so I got into affiliate marketing and started making money fast. Soon, I was making more than I thought I would. Recently, I found out that I am suppose to pay taxes on self employment income but I don’t know where to start.
Please help! How much will I owe in self employment tax, federal, state, and penalties all together?
Will I get in big trouble?
How do I go about paying my taxes. I am a little confused so I need as many details as possible.
Thanks!