Why isn’t fuel going to the carb?

My uncle had a Chevy truck. Driving down the raod, it died. Got it home and wasn't getting any fuel to the carb. Pull the fuel pump, replaced it and still no fuel. My dad looks in at the dash and says "Is your gauge working"?. Uncle says "Yeah, why?". Its on empty.

Watching 1 of these car shows and after putting the car together wouldn't start. Everything hooked up, 5 gallons of fuel, still no start. Turned out they had the line from the tank to the outlet and the outlet hooked to the tank side.