This will depend on whether you have booked a video or audio consultation. If it's a video consultation you will receive a push notification stating that your video appointment has started. Tap the notification and you can then enter the consultation where the clinician will be waiting. If it's an audio consultation it will start much like a phone call, you don't have to be in the app and you don't have to be looking at your phone beforehand. You can just tap to answer the call.