What can you do to help if you see somebody seizing?

911 & position them. Call 911 immediately. Lie them down on either side (with head support if needed) and their arms & legs bent so they are relaxed & loose. If not lying on the floor, ensure they don't fall from the couch or bed. Point their face downwards & flexed forward just a little so that a) they don't choke on their own saliva or bleeding from a tongue bite and b) they don't hurt their neck. Wait for help.
911. Call 911 or have someone call 911 for you while you try and help the seizing individual from causing any harm to themselves or others during the seizure. Help them to the floor and then lay them on their side so as to help with prevention of aspirating vomit. Grab an AED if available in case the person were to lose pulse and need resuscitation.
Protect airway, dial. Airway issues are critical. Patients may choke on their tongue or bite their tongue. They may aspirate. Use something safe (such as a popsicle stick) rather than your finger to clear the airway, to keep from being bitten. Be supportive in terms of preventing the patient from falling or injuring themselves. Call for help. Seizures have many causes, including hypoglycemia.