When an object is spinning, we say it has some angular momentum.

Angular momentum is something that is conserved - that means we can't just destroy. If something is spinning, it will keep on spinning until friction slows it down. So if we have a soccer ball flying through the air, and it's spinning, it's going to want to keep on spinning. This can be useful, because then the ball will have a more stable trajectory due to the spinning (since it can't just stop spinning in the air), and the kicker can make a more accurate kick.

The spin on a soccer ball greatly affects its trajectory, just like the spin affects nearly every flying object like a baseball, golfball, or Frisbee.To understand the reason why, we should think about how the air pressure surrounding the object depends on the spinning object. When you kick a soccer ball, it usually starts spinning due to the fact that your foot makes contact with different parts of the ball at slightly different times. Once the ball is spinning, the air pressure on one side is different from the air pressure on the other side of the ball. This is due to a well known theory called Bernoullis principle. This imbalance between the air pressure on opposing sides of the soccer ball imparts a force acting on the ball, which in turn causes the ball to move in a direction that is different from the initial trajectory.