Goals are added to or subtracted from a team’s final score if you bet on them, or the home team’s score if you bet on the draw. E.g. If the value is -1, that team will need to win by 2 or more goals for your bet to win.
For this one, you're betting on which team gets more corners in the match, after corners are added to or subtracted from a team's total. For example, a bet on Team A (-3) will win if Team A gets 4 corners or more than the opposition. Any corners awarded but not taken don't count.