Llamas are members of the Camel family. Technically, they are camelids.
In the Old World, there are two different camelids, the one-humped dromedary of the Arabian deserts, and the two humped Bacterian camel of the Mongolian deserts.
In the New World, there are four different camelids. Three are in the genus Lama: The llama, the alpaca, and the guanaco. One is in its own genus vigunae: The vicuna.
Both the guanaco and the vicuna are wild animals, and both have been or are endangered. Both have extremely fine fiber, the vicuna having the finest fiber in the world. The guanaco is somewhat llama sized, while the vicuna is a tiny, antelope like creature.
The llama and the alpaca are both domesticated animals, and have never been wild. The llama is considerably larger than the alpaca. In South American, llamas are used for pack animals, production of fiber for rugs and ropes, meat, and their dung for fuel. In South America, the alpaca is used for fine fiber production, meat, and even their dung is used for fuel.
In the United States, llamas are used for light draft, fiber production, show, companion and guard animals. Alpacas are used for fine fiber production and show in the United States.
Camelids are not ruminants, but they do ruminate. (I hope you don't find that as confusing as I do.) They have some differences from true ruminants, in that they have a three compartmented stomach instead of the 4 compartmented stomach of true ruminants, they have slower stomach motility, and their stomach movements are in the opposite direction to that heard for true ruminants. However, in terms of feeding, this boils down to the fact that they should be fed and treated as ruminants rather than as non-ruminants (such as horses). For example, oats should not be fed to llamas or alpacas, as the "awns" on oats can cause them to be caught up in one of the stomachs that has saccules, and then cause ulcers.
The camelids are better at feed conversion than true ruminants as well. This means that it takes less feed to make more llama than it would a sheep. Camelids can survive on what would be considered something close to a desert for a sheep.
Camels and camelids have two toed feet, with a toe nail sticking out of the end of each toe. However, they walk on a kind of leathery pad, which gives them excellent traction. In addition, this characteristic means that llamas can "cruise" delicate woodlands with little or no damage to the environment.
All members of the camelid family have a bad reputation for spitting. What more experience has shown is that this type of behavior was developed for their interactions with each other, not as a way to gross out people. In fact, when camels and camelids are appropriately raised, they never spit in anger at people. (The big problem is making sure that you're not in the wrong place when a "food fight" breaks out between them....)