From the main workout screen, click any movement in the workout to see the guidelines - then you can swipe this away.
As you perform your sets or after the section of the workout is completed, enter your weights and click the dot to save each set.
Once you enter weights, you can click the three dots next to the set to add any notes you like.
Be sure to hit the Mark Completed button on the main workout screen once your entire workout is finished.
In future workouts, your previous results will be visible by tapping on the chart icon in the top of the detail section.