Car was running fine - shut engine off and went into a convenience store and when I came out it wouldn't start. I checked the spare fuse and all other visible engine connections, spark plug wires, etc. Thinking it might be either the fuel pump or the relay. How do you tell if it is the fuel pump or an ignition/spark problem? Is the fuel pump a hard job to do?

Fuel pump is an expensive but minor PITA. Worst part is getting the wiring connectors off!
You can jump the relay in the fuse block to see if it runs (with the key on). You don't want to replace a pump simply by guessing.
As always, you need to determine if the problem is 'fuel or fire'. Plugs firing? Getting fuel? Then go from there.