Answer:
They look similar but are two different animals.
A carburetor works off of what is called a venturi effect (fluid (air is fluid) traveling at high speeds causes a vacuum) and creates a suction on small ports that come from the carburetors bowl and pulls fuel into the intake air stream. Literally, a carburetor sucks.
A TBI or throttle body injection system looks like a carburetor and has throttle plates like a carburetor that meter air into the engine. The fuel however is injected, through usually 2 injectors, upstream from the throttle plates and does not rely on suction but rather fuel injection pressure. The fuel injection event is metered by the ECM which uses programed algorithms called fuel maps or fuel planes that say at a certain throttle angle (measured by the TPS), a certain operating temp, a certain ambient air temp, a certain barometric pressure, a certain engine speed, a certain engine load, and the list can go on depending on how complex the system is to include travel speed, mass air flow, tranny temp, and whatever else an engineer might decide to monitor or reference. All this is taken into consideration and the EMC pulses the injector for a set time. All of this is checked and rechecked hundreds of times ea. second. A complicated animal compared to a carburetor.