A coach is someone who will be doing most if not all training sessions and be more of a “technical” manager, focusing on drills, tactics and finer details. A manager is someone who manages not only the team, but the staff around him and had a much wider grasp on how the club is ran. It’s not as common anymore, but a manager years ago would be running the club from top to bottom. Including what food the players are, where they went for pre season, player transfers etc.