P.M.
Kids before the age of two or three exist on a different planet than the one with manners. Constant correcting and scolding will mostly just frustrate you all. Keep modeling good manners, and they will eventually start copying you.
Don't expect too much of toddlers. Throwing is a major developmental stage, and actually helps develop eye-hand coordination and gross motor skills. Many of them won't perfect their small motor skills for quite a while yet. Not their fault. And peacefully sitting for more than 5-15 minutes is unrealistic. What they can manage will vary from day to day depending on how tired they are, how crabby their day has been, whether they've been sick, are teething, have had enough exercise….
Put only a few bites in front of him at any time, allow him to practice with a spoon in a bowl of water between meals, have puppet shows with his favorite toys modeling good table behavior. And let him be his age. If mealtimes become a battlefield, he'll eventually develop other negative behaviors, which can include lack of enthusiasm about eating at the table and even lack of appetite.