Once you are ready to begin your workout, just tap the first exercise to see a video demonstration of it, read the exercise instructions, and see how many sets and reps of it you have to perform. Tap the amount of reps included in a set if you wish to update it. You can also record the weight you are using for each set. Once you have completed a set just tap "completed" to save your progress.
Once you've completed all the sets for an exercise, you will automatically be taken back to the main workout page. Rest while you select the next exercise and prepare to continue your session.
After completing all the exercises included in a workout, you will see a screen including information about your completed session and asking you for feedback regarding your session. Tap the "done" button on the top right corner to move back to the main app page.
If you want to see and manage past or future workouts, you can browse through your schedule by tapping the arrow icons left and right of today's date.