1. Add gas: This is the most obvious step. Add enough gas to get the fuel pump to prime (usually at least a couple of gallons).
2. Turn the ignition on (but don't start): Let the fuel pump prime. You might hear a whirring sound from the fuel pump in the back of the vehicle (near the fuel tank) for a few seconds. This is normal. If you don't hear anything, you might have a fuel pump issue *in addition to* being out of gas, and you will need a mechanic.
3. Try to start the engine: If the pump primed, the engine should start normally.
If it doesn't start after adding gas and allowing the fuel pump to prime:
* Check for other problems: Running out of gas sometimes disrupts other systems. There's a small chance you have an unrelated problem (like a dead battery, faulty ignition, or other mechanical issue).
* Wait a few minutes: Sometimes, after adding gas, the fuel needs a little time to reach the engine.
If it still doesn't start after trying these steps, the problem is likely not simply running out of gas. You'll need to troubleshoot further, potentially requiring a mechanic.