To use an analogy of water in hoses, there are three tubes in a power circuit. There's a "hot" one, colored red or black. There's a "neutral" one, colored white. And there's a "ground" one, colored transparent or green.
Under normal circumstances, the "hot" and "neutral" forms a continuous loop. But the pump that moves the water is connected to the "hot" hose. It alternates between pushing water out and sucking it back in. The "neutral" hose comes back from whatever is using the water and empties out into the tank that the pump uses as its water supply.
As long as the loop stays intact, anything the pump pushes out to hot will come back around in the neutral and get dumped back into the tank. Anything the pump sucks out of the hot will come back around from the neutral and get sucked out of the tank.
If you cut the neutral hose, the hot hose can still work, but only if you have a water reservoir at the other end big enough to accommodate a complete cycle of pushing and pulling. The pump operator doesn't like this too much, because it makes them reliant on customers to keep their water tanks in good condition, and if one gets damaged out there, the pump can't work as efficiently, and it could get damaged too. It's just safer for them to provide a second hose back to their own water tank.
But if you cut the hot hose, breaking the loop, neutral's got nothing. The water in it just sits there. This is where the ground hose comes in. It is also shoved into the water tank at one end, same as neutral. It's sole purpose is to complete a loop back to the water tank in case the regular loop fails, so that water doesn't spray too far or let air get into the pump. Ground is the emergency backup return path.
Connecting electrical wires to a ground rod pounded deep into the earth is like sticking the loose ends of your hoses in the ocean. You can pull as much water out of it as you need, and dump as much into it as you need. Sea level stays the same.