English (Side Spin)
Hitting left or right of center curves the path off the rail and changes the angle off the object ball.
What side spin actually does
Striking the cue ball left or right of its vertical axis puts side spin, commonly called English, on the ball. On a clean, direct shot into an object ball, sidespin has only a small effect on the object ball's path (a slight throw), but its big effect is on where the cue ball goes afterward — especially off a rail, where the spin grabs the cushion and alters the rebound angle.
English off the rail
Running English (spin in the same direction the cue ball is traveling along the rail) widens the rebound angle, sending the cue ball off the cushion at a wider angle than a plain hit would. Reverse or "check" English narrows the rebound angle, holding the cue ball tighter to the rail path. This is the main tool for steering the cue ball around the table after it contacts a cushion.
The risks: squirt and throw
Side spin makes the cue ball veer slightly off your intended aiming line as it leaves the tip, an effect called squirt or cue ball deflection, which grows with more spin and a slower-pivoting cue. It also increases throw on the object ball at contact. Because of these side effects, most instructors teach beginners to solve position with speed and vertical spin first, and add side spin only once the simpler tools are not enough.