If you had a net profit from the self-employment on Schedule C Line 31 then you would have had Self-Employment taxes (Social Security and Medicare taxes) reported on your federal tax return.
The SE taxes are calculated on Schedule SE. The amount from Schedule SE flows to Schedule 1 Line 4. The total from Schedule 1 Part II Line 21 flows to your federal tax return Form 1040 Line 23.
If you did not have a net profit then no SE taxes would be entered.
