Hi,

In pen and paper mode test one need to fill his roll number, set of paper etc. Similarly when the computer based test are taken the PC already shows  your login id or name or both . You need to enter either your roll number or password. The conductor at the centre before commencing the exam gives the guidelines about what to do and what not to do. So don't worry. When you will reach the exam centre follow the guidelines given. If you didn't understand something you can ask them for help.

Hope you find it helpful.