How do I prime the engine

You don't need to prime the engine. If you turn the key to on position it turns on the fuel pump and primes the lines. You need to borrow/rent a fuel pressure gauge from a auto parts store like autozone, o'Reilly, etc. It should have a fuel pressure test port on the fuel line. If you turn the key on it will send power to the fuel pump for 2 seconds. When you crank the engine over it will send power to the fuel pump as soon as it detects oil pressure. You can look up the fuel pressure on the internet. You also need to verify that you have spark. I would also recommend checking for trouble codes, you can get a code reader at one of the auto parts stores. You can borrow them with a deposit. I can give you more information if you tell me what engine you have in the vehicle and the symptoms. And if you can give me the trouble codes and see if it has spark and fuel pressure.