Every workout plan (premium feature) starts off with a fit test to determine how fit you are and how intense the workout plan should be for you. The fit test should be the first workout you do, and after completing the fit test, Fitness Buddy will prompt you to relax for the rest of the day. The next workout is scheduled according to the schedule plan you set when choosing that workout. So, on the next day according to your weekly plan, the next workout will be ready for you!
If you completed the fit test and the workout plan does not advance, try force quitting the application and making sure that your device is connected to the internet. You can force quit by double tapping the home button and swiping up on the Fitness Buddy window.