You need to put the rubber parts into the mounting lugs on the servo case. Then you insert the brass grommet from underneath up through the rubber bushing. When you install the servo you want to mounting screws to just touch the rubber of the bushing. Many will just tighten the screw as far as they will go, but this will actually damage the servo. If you do this the rubber will no longer be able to absorb the vibrations from the plane. But it you tighten until the screw just touchs the rubber, the rubber will be able to isolate the servo from the vibrations.

Ken