You don't have to file an income tax return if you make less than the minimum income requirement for the tax year. For 2013, that was $10,000 for single filers and $20,000 for married filing jointly, but only $3,900 for married filing separately. The minimum filing levels are slightly higher if you or your spouse is 65 or older [source: IRS]. If you are claimed as a dependent on someone else's tax return, then your minimum filing requirement is $6,100 [source: TurboTax]. The levels go up every year with inflation, so make sure to check the current figures.
But even if you don't have to file a tax return, there are times when you should anyway. If your employer withheld taxes from your paychecks, you might be entitled to some of that money back. Plus, it's good practice for when you're working full time and have more income to declare.