Once a labor certification has been approved and a Visa number becomes available you may file the green card application. This may be done by applying for an Immigrant Visa (if you are outside the US) OR for an Adjustment of Status (if you are in the US and eligible to adjust). During the process of the application you may request a temporary work authorization so you can start work before your green card application is approved. You must not leave the US until your green card application is approved. If you do leave before you get the green card, your application may be denied. There is an exception to this rule and you may get a special permission to leave the US for a short period of time in cases of emergency. Except in rare cases a green card through employment does normally require personal interview.