While the pull-up may be one of the toughest exercises you can think of, it is a very important movement.
It strengthens muscles of the back as well as the biceps. The grip is also magnified when using the pull-up.
Most people however, cannot do a pull-up or a chin-up.
Never fear, for there are other options as well as other methods to working up to doing pull-ups.
First, the difference between a pull-up and a chin-up. Both the pull-up and the chin-up involve pulling yourself up to a bar. A pull-up, though, is done with the palms facing away from you (an overhand grip) and a chin-up is done with palms facing you (underhand grip).
Many say that a chin-up is easier due to the fact that your biceps are able to contribute more to the lift. Although the biceps have an advantage, the abdominals must turn on in a chin-up in order to protect your back and keep you balanced while you pull.
If you abdominals are very weak, you may have a harder time with the chin-up. I recommend doing both the chin-up and pull-up because they work the body slightly differently. For the sake of simplicity, I will refer to both as a just a pull-up, even though there is a slight difference.
If you have a hard time doing a pull-up in general, there are a few options that you can use to work up to them. The first option is to use the lat pull-down machine to build up your strength in your arms and back. The core will not be used as a stabilizer during this movement so the lat pull machine does not carry over completely, but it will work the primary movers for the pull-up.