If you are a beginner then it’s very easy to understand. (Pardon me if I’m wrong but I just infer from your nick name) Most beginners cant serve heavy spin short since they haven’t trained to contact thin enough. So the difference is mostly in the amount of spin. The longer one just has more. You just gotta learn how to read the amount of spin on the ball.
For the side spin, contact on the side of the ball.
You need to be able to push it back first, or better, simply touch it first, before attacking it. Since it trains your feeling (of the spin, the trajectory, the contact point etc.).
It’ll take much longer time than you think. So be patient with your progress.