The main point of a carburetor is to mix the right amount of gas with air to get the get the correct air fuel ratio so that the engine runs properly. If there is too much air being mixed with the gas, the engine runs lean and it won't run and if it does, it will damage the engine. If there isn't enough air being mixed with the fuel, the engine runs rich. If the engine runs rich, it'll flood and not run at all. If the engine does manage to run, it smokes a lot, stalls very easily, and/or get terrible gas mileage.

All new cars are now equipped with Fuel injectors (see my fuel injector page for more information) rather than carburetors because they provide better much fuel efficiency and lower emissions. 

A lot of small equipment still do come equipped with carburetors because they are much more simple and cheaper to make. Things that still have carburetors are (but not limited to) lawnmowers, weedwackers, snowblowers, and chainsaws.

please view this video to see in depth how the carburetor works http://static.howstuffworks.com/mpeg/chainsaw3.mpg