what is the firing order and what is the purpose of flywheels and lifters

The firing order is the order in which the fuel charge is ignited in the cylinders. The lifters actuate the valves opening and closing them from mechanical interaction with the camshaft(s) and the flywheel does a couple of things. It connects the crankshaft of the engine to the transmission torque converter or clutch (automatic or manual transmission) and helps smooth vibrations. For a good read on an internal combustion engine go to the link.....https://en.wikipedia.org/wiki/Component_parts_of_internal_ combustion_engines