Use denture adhesive to strengthen the bond between denture and gum. Do not expect the adhesive to "fix" a poorly fitting denture.
Dental-Professional.com suggests, "Adhesives are a useful aid to denture retention and stability for all patients. They are particularly useful for patients with special needs e.g. poor neuromuscular control or dementia, but can offer advantages to all denture wearers."
Proper bonding between dentures and gums reduces the amount of food that can get under the denture, and increases confidence in the wearer.