If you have no FTP or Fitness Level set, the first time you open the Workouts menu, you'll see one of the following screens:
The Ride Fitness Level screen
The Run Fitness Level Screen
The Fitness Level preset screen gives you the option to choose a profile that's based on how often you ride/run and will then auto-populate an appropriate FTP value or pace. This is intended to help new Zwifters get a structured workout that's appropriate for them, instead of ending up with one that's too hard or too easy.
Just pick a profile based on how much you ride/run, and Ride On!
Q: How do I change my Fitness Level Profile?
A: If you know your FTP/pace times and missed entering them on the account creation screen, just choose the Custom profile option, and enter your FTP/pace times.
Cyclists: If you find that your workouts are still too hard/too easy, you may want to consider taking an FTP test for a more accurate measurement.
Q: How did you calculate the Fitness Levels?
A: While we won't reveal the specific formula used for calculating these presets, we take into account your profile factors, including height, weight, age, and gender to come up with an approximate value.
Again, this value is only intended as an estimate for getting started; you should take an FTP test if you want a more accurate measurement.