I like Aaron’s answer and would add that it also provides guidance by a professional on a safe way to exercise at a relatively small cost to the individual.
Here is a good article to expand on what the others have mentioned–it may help you.
An instructor-guided workout taught to a group of exercisers, to achieve one or more fitness goals (cardiovascular endurance, strength, flexibility). The exercises performed may have several options to accommodate varying fitness levels and physical limitations. Individuals who are newer to exercise or have significant medical conditions may benefit from the one on one attention of a personal trainer before joining group-ex classes.