If you have no other income except for self-employment, and your net income (profit after expense) is less than $400, you do not need to file a return.
If you have more than $400 of self-employment income OR your total income is more than the filing threshold for your status, then you must file a tax return and report ALL your income. (The filing threshold if you are single and someone else's dependent is $6300, and is $10,350 if you are single and not a dependent.)
When you have self-employment income, you owe 15% self-employment tax (the self-employed version of social security and medicare tax), plus income tax. The income tax could be between 0-25% depending on your total of all income.
You are supposed to file a schedule C for self-employment where you report your income, deduct expenses, and pay the self-employment tax. That information carries over to your regular tax return where you report any other income, your personal deductions, and pay the income tax on the overall total taxable income.
What Carl is suggesting is that if you have more than $6300 or more than $10,350 of total income, but your cam income is less than $400, there is a shortcut to report the cam income as "other income" and pay income tax but not self-employment tax. This would work as long as $400 is your gross income. If your gross is more than $400 and you want to subtract your expenses, then you still need the schedule C and to pay the self-employment tax on the net income after expenses. Because if you report "other income" you can't deduct expenses against it.
