Ask the other person to send you her/his tax information (SIN/Date of Birth, Address, T-slips etc.). Enter that in TurboTax. When return is complete, pay. Review it with the other person and have her/him netfile. You can prepare return on somebody else's behalf, but you cannot netfile any return but your own.
To start a new return, click on Tools (on top black bar) and select "Return Manager".
Hope that helps.