Closed-heel/full-foot fins have a foot pocket and an attached blade. They come in all sizes, and they are primarily designed for most applications where there is no scuba equipment and/or where the scuba equipment is lightweight for warm waters.
When the diver is wearing heavy scuba equipment with plenty of drag, most divers will choose open-heel fins because they provide more thrust. Closed-heel fins are good for warm-water boat scuba diving but not for shore entries when walking over hot sand and sharp rocks. They are also less durable and harder to use in strong currents. Consult the dive center and/or your instructor for advice.