It all depends on your game system (Vampire the maquerade/ or Requiem, D&D, Shadowrun) In all cases you need whats known as the Corebook, or Core Rule Book that explains all the basics. Its alot of reading. Im pretty sure there are Character sheet Generator programs available that can make it easy to fill in .
This could be done also in VTMR if someone actually felt like modding in the complete updated character sheets (the ones in WoDmod dont cut it anymore).
I know how to fill a character sheet, just dont feel like explaining atm because its alot of detail and I only know character sheets for Vampire the Masquerade and Shadowrun(and you didnt mention what you play)