um, we might need a better starting point than that. what _do_ you know? what are you trying to do?
Some EGR valves are vacuum actuated - they have a diaphragm which is exposed to manifold vacuum on one side and air on the other. Vacuum hoses connect from the manifold to a solenoid, and then from the solenoid to the valve. When the solenoid opens, the vacuum sucks on the diaphragm and opens the valve to let EGR into the intake manifold.