When you place a handicap bet (“+” or “-”), the team/player starts with an advantage/disadvantage. In order for the bet to be a winner, the team/player must score more goals/points so that they achieve the desired result with the chosen advantage or disadvantage.
Example: “Manchester United -1” means that the team starts from scratch with a handicap of one goal. For the bet to be a winner, Manchester United must win by a difference of two goals. Basically, the handicap or spread is added to the score at the end of the game and the final result must be in favour of the team you bet on.