Now that you've cast on your stitches, you're ready to actually begin forming the knit stitches. Put the needle with the stitches in your left hand and the empty needle in your right hand. Hold the needles however feels comfortable for you.
Place the tip of the right needle into the stitch at the top of the left needle from front to back, wrap the yarn coming from the ball around the right needle counterclockwise, then pull that loop of yarn through in front of the left needle and slide the original loop off the left needle (or read more detailed instructions on forming the knit stitch, with pictures).
Continue in this same method until all the stitches from the left needle have been worked and are on the right needle.
As mentioned earlier, don't worry if your stitches aren't even and perfect; that will come with practice, which is what we're doing right now.