Simple answer: $12,200 the filing threshold for a single person who is not somebody else's dependent. That's when you have to file.
But taxes aren't simple. If you have more than $400 of self employment income, you have to file. Dependents with unearned income have to file at $1100. There are refundable credits available to people with earned income who are not required to file but should. You will want to file to get back any withholding in box 2 of your W-2.
There is no minimum you have to make to file, when not legally required to. The earned income credit starts at $1 of income and the refundable portion of the child tax credit starts at $2500.
