What is the thermostat dial for? I want hotter water, so I turn the knob to 150. Yet cold water is still coming out.

Some A.O. Smith storage water heaters have an external knob or dial to directly control the heater thermostat.  The set temperature (usually in °F) approximately controls the maximum temperature of the water stored in the water heater.  You don't have to set the knob to 150°F to get hot water.  If the water coming out of your heater outlet is just as cold as inlet water, then your water heater maybe non-functional due to several possible reasons, including lack of electricity or gas, or busted heating element or other parts.