I don/t have a business license, but made a decent amount of money being a fitness trainer. How would I file that income this year? Self-employed or extra taxable income

If you have Self Employment income you have to file a schedule C in your personal 1040 return. You may get a 1099Misc for some of your income but you need  report all your income.  So you need to keep your own good records.

Here is some reading material……

IRS information on Self Employment….
http://www.irs.gov/Businesses/Small-Businesses-&-Self-Employed/Self-Employed-Individuals-Tax-Center

Pulication 334, Tax Guide for Small Business
http://www.irs.gov/pub/irs-pdf/p334.pdf

Publication 535 Business Expenses
http://www.irs.gov/pub/irs-pdf/p535.pdf

Self Employment tax (Scheduled SE) is generated if a person has $400 or more of net profit from self-employment on Schedule C.  You pay 15.3% for SE tax on 92.35% of your Net Profit greater than $400.  The 15.3% self employed SE Tax is to pay both the employer part and employee part of Social Security and Medicare.  So you get social security credit for it when you retire.  You do get to take off the 50% ER portion of the SE tax as an adjustment on line 27 of the 1040.  The SE tax is already included in your tax due or reduced your refund.  It is on the 1040 line 57.  The SE tax is in addition to your regular income tax on the net profit.