Every exercise has a style, and it decides whether you are describing one movement or several performed as a group. The same two options exist in the Coaching app on your phone, under the same names.
Conventional
Ideal for conventional exercises such as multiset routines. One movement, a number of sets, a target and a rest period. Back squat, 4 sets of 6, three minutes rest.
This is the right choice unless you specifically need the other, and it reads most clearly on a client's phone.
Versatile
Ideal for advanced methods like supersets, tri-sets and cluster sets. Rather than one movement you build rows (add a row per movement, remove ones you do not need) grouped under a single heading.
That heading is the exercise system title, described as a label for the included exercise collection. Name it so the method is obvious: "Superset A", "Push tri-set", "Cluster: 5×2".
That title is what your client reads above the group on their phone. It is doing work on their screen, not only in your own library.
Choosing between them
Ask whether the movements have to be done together to make sense. Two exercises that merely sit next to each other are two Conventional exercises. Two the client alternates between without resting are one Versatile group, and entering them separately loses the very thing that makes it a superset.
The same logic applies to a cluster set, where the rest sits inside the set rather than after it. Described as a plain multiset exercise, that intent disappears.
Either style counts as one exercise inside the workout. It takes one order number, lowest first, and sits in the sequence like anything else.
A caution about over-using Versatile
Grouped rows are denser to read on a phone and harder to log against. A whole workout built out of them costs the client something every time, where it cost you the effort once. Use it where the method genuinely requires it rather than as a default.
If a client keeps asking how to perform something, the style is often the reason: either a group that should have been separate exercises, or separate exercises that should have been a group.
Where to go next
Adding and editing exercises covers every field on one of these: title, sets, reps or time, rest and weight. It also covers the two switches that decide what your client can log back. Building a workout in Basecamp covers the workout they sit inside.