If you have a workout to do today, then you can find it in the ‘Today’ home tab. If you’ve scheduled in a workout plan, but you don’t have a workout this week, you can scroll left/right on the calendar to navigate across weeks and find your workout plan.
If you’d like to find a workout to do, go to the ‘Explore’ tab, and look through the workout plans, and you can tap on individual workouts to do them from there.
Once you're in a workout, you cannot exit it until you've completed it (or saved your progress on it). So make sure that once you begin a workout, you have enough time to complete it fully.