What does it mean when truck wont start unless you spary eather in carburetor?

More then likely The fuel pump has quit pumping fuel. Possible cause: Fuel pump relay,Fuel pump fuse, Bad fuel pump stopped up fuel filter, Not enough fuel pressure. If it's fuel injected then it should be no lower are higher then the factory FUEL PRESSURE SPEC'S.

It would help alot to know what you are working on. Year, engine size and what it is. Does it have fuel in it, for SURE ? Check fuel pressure with fuel gauge. Very important to check with a GAUGE.