An agonist superset is also known as a "compound set." This type of superset consists of simply combining a primary muscle exercise with an assisting muscle exercise. For instance, an agonist pairing superset could be a one-two punch of pull-ups and biceps curls (see video), or a dumbbell bench press followed by a dumbbell flye.
In the video, the pull-ups act as a primary muscle exercise (back), while the biceps curls act as an assisting muscle exercise.
Because of the metabolic and muscular damage (both good) that'll result from these supersets, you'll need longer rest periods during the workout and longer recovery periods between training sessions for the same muscle group... which is perfect if you're a busy guy who can only manage 2-3 gym sessions a week.