In the western Pacific or Indian oceans, it’s called a typhoon. In the Atlantic, it’s a hurricane. They’re the same thing, they’re just regionally named.
Now, how do they form? Tropicalweather.com explains that there are seven conditions that could cause a hurricane or typhoon to form: a pre-existing disturbance, warm ocean water, low atmospheric stability, sufficient Coriolis force, moist mid-atmosphere, and upper atmosphere divergence.
(Those are discussed in greater detail here).
The afore-linked websites are a bit wordy. So, in layman’s terms:
Tropical storms always occur in the tropics because they need ocean water of 80 degrees or higher to form. Because of the hot water, the air directly above is warm as well and as we know, hot air rises.
As this hot air rises, it leaves behind an empty space (a low pressure system) where it used to be. This void becomes a vacuum of sorts and sucks in more air, which eventually warms and rises, too.
The air cools as it rises and condenses into moisture, creating clouds. As these clouds form, and more and more air is circulated and pumped up, the system begins to spin.
(Interesting fact: in the Northern hemisphere, hurricanes rotate counterclockwise. In the Southern, they rotate clockwise).
More and more air is pumped in, warmed, and circulated throughout the system, and the storm grows in strength and size and moves across the ocean. Once it is on land, however, there is no more warm air to feed it and so it eventually dies.
Hurricanes/typhoons are rated according to their wind speed. A category 1 hurricane has wind speeds of 74-95 mph. A category five, the worst kind, has winds over 155 mph.