You and every family member between 14 and 79 years that is on your application needs to take a photo and fingerprints. That is called "biometrics".
You cannot just take the photo yourself, you need to do it on an authorized service point. And before you can schedule an appointment, you need to receive a request from IRCC.
After you pay the biometric fee during your application, you will receive a letter (message on your account) asking for your biometrics. After you received it, you have 30 days to do it.
The next task has instructions on how to proceed after you receive the letter.