The word "bongos" is often used (out of ignorance) to refer to many kinds of drums that are, in fact, not actually bongos. I have heard congas, djembes, tablas and even tom-toms referred to as "bongos". They are not the same-- not even close.
Bongos are two small drums which are attached to each other. The two drums are of equal height, though the diameter of their drum heads differ. The larger drum is called the hembra, the diameter of its head usually ranges from 8 to 10 inches. The smaller drum, the macho, has a head 6 to 8 inches in diameter. Bongo heads can be made out of a variety of animal hides. Synthetic heads are also popular. X-ray film is often used for the drum head in Cuba; it creates a distinguished "popping" sound with little resonance. This sort of sound is highly desirable for the macho drum, though is hard to achieve with regular skins as they tend to snap under high-tension tuning. Furthermore, change in temperature and humidity can cause a tuned head to snap due to physical constricting. For this reason, it is wise (though pesky) to de-tune your drums after playing them. Tuning the drum is mechanically simple, as most modern bongos are fitted with steel hardware which can be adjusted with a crescent wrench. However, this hardware was not always a standard: earlier in the 20th century, skins were tacked on, and had to be heated manually by flame to be tuned. Bongos are most commonly made out of oak or fiberglass, though it is not rare to find them made out of other kinds of wood.
Bongos are played with the macho to the left of the bongocero (bongo player). They are held between the legs and struck with the pads of the fingers--slapping knuckles against the heads can cause serious physical damage to the player (though makes a much louder noise). The macho drum is usually played more than the hembra. The hembra serves as a "bass" of sorts, the macho acts to accent and count out time.
Bongos are most commonly used in Afro-Cuban music, though they really could go with any genre of music: I've played along with everything from ambient to industrial to country to classic rock to indie pop. They are extremely portable--bongos weigh about as much as an electric guitar (though are much less comfortable to carry around).
You should take up bongos. They're great. I swear.