Hello @Nikki88,
The only way to take a photo using the App on your phone is as a step in a process, such as the process of uploading a photo of government ID or of validating your ID. You must start these processes by going to the Airbnb website airbnb.com or whatever your country specific one is. Once you start the process on the website you'll be given the option of taking any needed photo via the app on your phone or continuing on your laptop and using the browser to take it via your laptop camera.
If you choose the app option you'll receive an app notification or SMS text message with a link. Tapping on the link will start the phone camera with a photo template overalid on the screen to guide you as to where your head should be in the frame.
For example, I recently clicked to validate my ID, choose the phone app option and immediately received an app notification and SMS text message. I opened the app notification and immediately the front camera started and there was an oval on the screen. I moved the phone so that my head appeared within that oval area and then tapped on the icon to take the photo.
A few hours later I received an email saying that the verification was successful.
Steve.