I am going to show you how to throw a slider. I have read that you should not throw this pitch unless you are 15 beacause you could hurt your arm. I am 13 and I throw sliders all the time and I have only hurt my arm once. You try this pitch at your own risk.
Step 1: The grip
For the grip hold the ball like how I did in this picture (Sorry I used a left handed grip). Put pressure on your thumb and middle finger. Then you just throw the ball.
Step 2: The beginning of it
As you can see this ball is going rite down the middle for a strike.
Step 3: The effect of a slider
As you saw in the last picture the ball was going to be a strike but in this picture it curved as soon as it reached the plate. Now you can see that I never really pitched the ball I was just holding it in my hand the whole time but if I did pitch it the ball would curve alot.