As the compressed air comes out of the turbo it is very hot. It is routed
thru an intercooler (radiator) to cool down the air before it goes into the
intake manifold. It's there to help make a few more hp.

Denny

Also called a charge air cooler, it cools off the hot compressed air from
the turbocharger (because whenever you compress air, you raise it's
temperature), before feeding it into the intake manifold (because colder air
is more dense, and therefore gives you more oxygen in the cylinders to burn
more fuel, and make more power).

If you look on the passenger side, you'll see how the discharge pipe from
the turbocharger goes into the passenger-side of the intercooler.  On the
left (driver's) side, you'll see a pipe that brings that air from the
intercooler up into the intake manifold.