You've just started working on a slider, right? That is not a pitch you can get overnight; even if you can get the hang of it in a few minutes it will take some months before you master it and can get it to do what you want it to. I got the hang of mine in about ten minutes, but I spent eight or nine months getting it down cold because it was going to be my strikeout pitch. And a good one it was. So let me tell you a couple of things about that pitch.
First, the grip. It's decidedly offcenter; you grip the ball with the index and middle fingers close together, the middle finger just touching one seam and the thumb resting on the bottom seam for support; a lot of pitchers have the two other fingers curled up on the other side of the ball. Don't grip it too tightly, because you don't want to squeeze the juice out of it! Then you throw it---yes, you're a sidearmer, just as I was, and you'll find it a lot more comfortable. You ease up on the wrist action---think of a chef flipping a pancake or a crepe (yummy); my wise and wonderful pitching coach told me, "Throw it like a curve, but roll your wrist, don't snap it." Don't worry about the strike; it will come, and the slight pronation occurs naturally so don't even think about it. Just work on the location---the control---and take your time. Before you know it you'll have a nice slider in your arsenal---and because you're a sidearmer you'll be able to keep the ball down. So go to it, and all the best.