You got it. Say you make $14×40×52 = $29,120 for the year. Subtract $19,400 standard deduction. 10% of the $9,720 left is $972. That's your tax before credits.

Now subtract credits; it's not $4,000 since your lower income lowers it, but you get Earned Income Tax Credit with that low income, so I'm computing $6,700 "refund" even though you paid $0.