To be certain, you'll need to:
1. Consult your owner's manual: This should have a diagram showing the location of major components, including the starter.
2. Look for a large, cylindrical component: The starter motor is relatively large and easily identifiable. It will have thick cables connected to it, usually one large positive cable and a smaller negative cable.
3. Use a flashlight and possibly a mirror: The area around the starter can be cramped, so you might need a light and a mirror to see it clearly.
4. Search online for a picture: Search for "1992 Ford E350 [engine type] starter location" on Google Images or YouTube. Seeing a picture of the engine bay will help you locate it.
Caution: Working near the starter motor involves working with the battery and high voltage. Disconnect the negative battery terminal before working on or around the starter to prevent accidental shocks or short circuits.