To fill out a passport application form online, visit the Passport Seva Portal and register as a new user. Select "Apply for Fresh Passport/Reissue of Passport" and click the link to access the online form. Provide applicant details like name and date of birth, as well as family details, present address, emergency contacts, references, and previous passport information if applicable. Submit the completed form and then schedule an appointment to visit the Passport Service Kendra.