If you are not working, the court can calculate your child support based on the presumption that you can earn minimum wage at 40 hours a week. This does not apply if you are in jail or prison and will be there for more than 90 days.
If you are intentionally unemployed or underemployed (not working to your full potential), the court may set the child support on your earning potential. The court may look to past earnings to make this decision. You should talk to a lawyer if you think the other parent is intentionally unemployed or underemployed.