Exercises sit inside workouts and carry the prescription your client works to. Basecamp explains several of the fields more clearly than the phone does, which makes this the better place to set them up properly the first time.
The prescription
Title, sets, reps or time, rest and weight. Each of the last three carries its own unit, so you can prescribe 45 seconds or 10 reps, 90 seconds or 3 minutes, kilograms or pounds, without doing conversions in your head.
Order works the same as on workouts: a number, lowest first. Notes carry your cues. The same rule applies as everywhere else in the product: notes must not contain personal or private information.
The two switches that change what comes back
Comprehensive updates. Basecamp's explanation is the clearest version of this in the whole product: your client logs the weight and reps they actually managed on each set, instead of only leaving a note.
Leave it off and the only thing that comes back is written notes. Turn it on for anything you want to progress by numbers.
Unilateral updates. For single-arm or single-leg work: your client logs left and right separately.
Turn it on where the two sides genuinely differ and leave it off elsewhere. It doubles the logging on every set, which is worth it for a split squat after an injury and pure friction on a barbell row.
Video
Search your own library by name and attach a clip, or paste an external link. Basecamp is explicit about what that second option means: a demonstration hosted elsewhere, for example on YouTube, and external links are subject to review.
Attaching from your library is the better option where you have the clip. It cannot be taken down by somebody else, and it does not put an ad in front of your client mid-workout.
What the sidebar shows you afterward
Each exercise carries small badges summarizing how it is set up: whether it has a video, whether it is unilateral, whether detailed logging is on, its sets and rest. Useful for scanning a workout you built weeks ago without opening every exercise.
Alongside them sit views and completions, and when the client last viewed it. An exercise with views but no completions is one somebody keeps looking at and not doing. That usually means it is unclear, too hard, or needs equipment they do not have.