1.> Visit the NYSC website www.nysc.gov.ng and click on the link "Prospective Corps Member" or click on the link below
http://portal.nysc.gov.ng/PrePayment.aspx

2.>Fill in your necessary data.
The following are the data required to be supplied by you.
Names(Surname Other names): e.g. Umukoro Eseoghene Gift
Email Address:
Confirm email Address:
Password:
Confirm Password:
GSM No:
Graduated from: Choose Nigerian Institution or Foreign Institution as applicable
Programme: chose whether your Programme in tertiary institution was a Part-time or Full-time programme.

Finally, click on the continue button


For more help, and a graphical step by step procedure
visit the source here