You can find a "Prepare" item located in the action menu of a programmed workout (one that's been added to the calendar). "Prepare" takes users to a workout screen that contains valuable information like movements, recent posts, and a percentile slider. The idea is to provide information that may help users "prepare" for the day's workout.
The percentile slider is shown automatically on workout screens that have accumulated enough results from the btwb community. If you don't see a slider, btwb doesn't have enough data yet. The slider lets users discover scores for specific percentiles. For example, someone can use the slider to view the 75th percentile score, then use that as motivation to push a bit harder on the workout.