The Neutral and Ground are generally connected together at your service panel, not at your devices.
At the device, neutral is the path for return current. All the current that comes "from" the hot leg "returns" through the neutral wire. I'm using quote marks because current actually alternates directions in an AC system. Hence the name AC!
Anyway, the ground wire should only carry current in the case of a fault condition. In the USA, residential ground wires are often just bare, uncovered copper. When plugging in a grounded appliance or other device, the ground wire gets attached to the chassis.
Say, for example, that the insulation on your hot wire gets damaged and the conductor comes into contact with the metal body of your washing machine. The current shorts through the chassis and then through the ground wire. This high current causes your circuit breaker (or fuse) to trip. If you didn't have the ground wire then the mains voltage would electrify the entire chassis. Then the next person touching it becomes the return path :)