The long-tail cast-on technique can be difficult to learn. The drawings of this multistep technique in knitting books can be hard to follow along. A better solution may be to visit a craft or knitting store and find someone to show you how to cast on. Also there are Web sites with pictures, photos, and even video demonstrations.
Hold the ball of yarn in your lap. Drape the yarn over a knitting needle, and secure it to needle with that hand's index finger.
With your other hand, wrap the yarn coming from the ball over your index finger. Hold the end, or tail, of the yarn over your thumb. You will need enough "tail" to make all the stitches needed to cast on, but for purposes of practice, simply make sure you have 12 inches of tail hanging over your thumb. Wrap the rest of your fingers over the two ends of yarn and pull to provide tension. Let's call the horizontal yarn going over the index finger the "top yarn." The yarn coming in front of your thumb is the "thumb yarn."
Move the needle toward your thumb, which forms a loop of yarn around your thumb. Insert the needle under the thumb yarn.
Then pull the needle toward your index finger. Place the needle up and over the top yarn and pull the top yarn back through the loop of yarn on your thumb.
Snug the yarn down on the needle, removing slack. You have two cast-on stitches on the needle.
Repeat Steps 3 through 5 to make a third cast-on stitch.
Continue repeating Steps 3 through 5 until you have become comfortable the technique. Remember to keep an even tension in the cast-on stitches.
Once you have mastered the technique, you can use it to cast on for your next knitting project. Pull out enough yarn to allow about 1-inch per cast-on stitch required for your project. For example,100 cast-on stitches would mean pulling out about 100 inches of tail. This is a generalization, and the amount of yarn will vary depending on the type of yarn you use, your needle size, and the tension with which you cast on. If you pull out too much, you can always trim the end off. If you do not pull out enough, you will have to start over.