If your annual earnings exceed £5,725 you will have to pay NIC Class 2 (£2.70 per week).
If your annual earnings exceed £7,755 you will have to pay NIC Class 4 (9% of income after £7,755) as well as paying the NIC Class 2 (£2.70 per week).
If your annual earnings exceed £9,440 then you will also have to pay income tax on the money earnt after that.