However, a visual inspection is absolutely crucial. The exact location can vary slightly depending on the engine type (e.g., a 300 inline-six will have a different location compared to a V8). Locate the engine and search the top carefully for the oil fill cap.
If you're unsure, consulting a repair manual specific to your van's engine is the safest bet. You can also find diagrams online by searching for "[your engine type] oil fill location" (e.g., "Ford 302 V8 oil fill location"). A picture is worth a thousand words in this situation.