The fuel pump relay should be found in the under hood relay center. Properly testing the relay can be complicated. You will need a wiring diagram and some basic electrical skills to properly diagnose the relay. I am assuming your fuel pump is not working correctly. You may save money in the long run by having a qualified technician diagnose the fault with your 1995 Chevrolet Astro van.
The relay is located outboard on the firewall next to the master cylinder. There are probably a mess of wires hiding it. There are two relays - the one next to the master cylinder is the ASD relay and the other is the fuel pump. Have someone turn the ignition switch to the on position while you hold on to the relay. You should feel it click when the ignition is turned on, if not it is probably bad.