Making cuneiform wedges can be tricky at first, but it gets easier with practice. To do it you will need some soft clay or plasticine and a stylus with a square cross-section and crisp corners. The wrong end of a chopstick works well. You need to press the corner into the clay so that only 3 face are touching the clay. This will make a triangular impression. If you press it in at the wrong angle, you will get a rectangle, not a triangle.
All cuneiform wedges are made in this way. You just need to rotate the stylus or the clay so the triangles point in different directions. Sometimes you might see signs with wedges are wider and look more like corners than points. These are called Winkelhakens but you make them in exactly the same way: just experiment with the angle of your stylus till you get the hang of it!
