Association Football (soccer) is played by two teams, each of 11 players, who attempt to get the ball into the opponent's goal, usually by kicking it.
What does "to get the ball into the opponent's goal" mean ?
This is a tricky sentence to understand, because I think this "get X into Y" is actually not the phrasal verb it looks like (which would be to get into something).
"Get" has many definitions, and I think the appropriate definition of "get" here is
5 b: to cause to move.
"Into" just means "towards the inside of something"; the ball is going into the goal because it is moving to the inside of the goal from the outside.
So the players are causing the ball to move into the goal. They could kick the ball into the goal, or carry it into the goal, or whatever, but get covers any possible way of doing it.