Tents are considered to be shelters and the components that generally make up a tent include sheets of material (e.g. fabric) attached (or draped over) to either a frame of poles (tent poles) or some sort of supporting rope. Smaller tents tend to be free-standing whereas larger tents may require anchoring with guy ropes tied to stakes (or special tent pegs). A guy rope is simply a tensioned cable to contribute stability to the tent. One end is attached to the tent and the other end is secured to the ground at a certain distance from the base of the tent with the tent pegs indicated earlier. A tent peg is a spike essentially, with either a hole or a hook on top end. It can be made from wood, metal, plastic or even some kind of composite material.
The initial purpose of tents was as a portable home for nomadic people in all parts of the world such as Mongolians, Tibetans and Native Americans. This of course has evolved to recreational usage (e.g. camping, festivals, weddings, major corporate events) as well as temporary shelters (e.g. in case on natural disasters, as excavation covers). Military forces are also using tents on a regular basis. This preference stems from that fact that tents are relatively fast to setup and dismantle when compared to the more traditional forms of shelters. The armies use tents for a variety of purposes including as sleeping quarters, dining facilities, recreational facilities, security checkpoints and tactical operations centers. For recreation, particularly in camping, tents are considered to be practical since they are portable and have low impact on the surrounding environment. In the case of natural disasters or other kinds of emergency, people may have lost their home and hence need a reliable shelter that can be quickly available to them, which tents are ideal for.
Tents exhibit an extensive range in sizes depending on the purpose. On one of the spectrum, there are one-person shelters designed for a hiker as a form of accommodation. On the other end, you can have circus tents that can hold thousands of people. In recreational camping, size is used to categorize tents and there are two classes. Smaller tents have been designed with weight as a primary consideration. Such a tent is small and light enough to allow a person to carry it over long distances (e.g. backpacking, touring bicycle and boats). The second class is the larger tents (e.g. 4 man tent). They are much heavier and likely require a vehicle (e.g. four wheel drive car) to carry them.
Now that concludes the overview on the different tents you can get.