Where is the carbuerator on a 1997 Nissan Sentra?

The 1997 Nissan Sentra, like almost all passenger vehicles made since the late 1980s, does not use a carburetor. It uses fuel injection.

Instead of mixing air and gasoline in the carburetor, then forcing that into the cylinder, the air is forced into the cylinder by itself, then gasoline is squirted into the cylinder by the fuel injector. There is one injector for each cylinder, and they are fed gasoline through a "fuel rail", which is a tube where gasoline is pumped from the gas tank to the engine, across all of the injectors, and back to the gas tank.