You will see interview appointment slots immediately after securing a biometrics appointment. It is important that you schedule both during the same web session. If you only schedule biometrics but not the interview, the biometrics appointment with be automatically cancelled.
Every step from here until you are finished is driven by you. The Manila embassy will not be scheduling or emailing you anything for K-1. Not all embassies do things the same way, but for Manila, you make your own appointments for biometrics, interview, and medical.