Inlet tank: Coolant enters radiator here via a hose; Core: Coolant passes through water tubes where heat is removed via cooling fins and air passing through the core matrix.
The traditional radiator is a Down-Flow type which has the inlet tank at the top and outlet tank at the bottom. Another common form of radiator in current use is the Cross-Flow type in which the inlet tank is on one side, the core beside it and the outlet tank at the other side.
Read more about Overview of Down-Flow, Cros-Flow and Multiple-Pass Type Radiators
Use of coolant; Radiator servicing; What to do if your car overheats; Causes of premature radiator failures.