Turbos are pretty simple, but often misunderstood. They are basically a low-pressure air compressor that uses the engine exhaust to power the compressor wheel. Exhaust gas goes in one end of the turbo, spins the compressor blades, and then exits the turbo heading towards the tailpipe. On the other side, it needs an air input, and then an outlet to the engine after the air is compressed. Also, it shares oil with the engine, so it needs an oil input (from the oil pressure sending unit) and an oil outlet (going back to the oil pan).