This is the exercise that helped me expand my capability to play with all four fingers on the fretting hand. (some folks only like to play with three, but why waste that extra digit?) For beginers, I suggest doing it very slowly and in a very calculated manner. Don't worry about how slowly you're going. Speed and dexterity increase with practice. This exercise will acomplish several important things. You'll utilize all four fretting fingers, it will stretch you out and enable you to increase your strength and it will get you used to transitioning between strings.