Whats the purpose of a earth probe (metal pole in physical ground of earth) in your home ?

 

If you didn't have one, it would be likely that when you're washing your hands or showering that you would feel a lot of little electric shocks. The earth ground eliminates any induced charges in water pipes, especially, but also protects you in case a wire comes undone or something and contacts more metal. The ground probe keeps the current from going through your house, and potentially, from going through you.
These are two of the main reasons why your house has an earth ground.
Der Strom

 

The earth ground rod(s) is/are connected to the Neutral line at the electrical distribution panel., and to the ground (earth) connection at wall outlets.

In case an appliance develops an electrical defect where the 'hot' lead is shorted to the appliances' case, the ground/earth connection protects the human that is using the appliance. Shorts to the earth ground will cause the circuit breaker or fuse to open in a very short period of time. Without the presence of the ground, the human could be exposed to mains power, which would most likely be fatal.

The Neutral line from the power company is grounded at the power distribution panel in case the power company's transformer develops a fault. Without that ground, the mains voltage might be connected to the very high voltage on the primary side of the power company transformer; in the States that could be 11kv to 22kv, or even higher. With the earth ground present on the neutral line, the fuse at the transformer would open up in a very short period of time, protecting the home.

Many years ago, water pipes were used as electrical grounds. This practice was been discontinued quite a few years ago in the States, as water pipes are now made from non-conductive plastic materials.

 

Ok,but why does electricity try to go to ground into soil, gravel, stones,sand etc they are **** poor conductors and how does it return to its source ?

 

Ground rods are for lightning protection in home power systems and don't have current flow under normal conditions. The neutral/ground tie at the main panel does provide short protection inside a house but the current flow in this condition is not into the ground. Where you would have current flow in a rod system is when there is a direct strike (You would need a very good grounding system shunting current to stop damage in this case) or a strike near a building or electrical line and the ground potential rises in relationship with another location that is grounded to earth. When this happens it's important to have a good earth ground so the current from that rise can be safely shunted outside the internal electrical wiring. So the earth ground at that point doesn't have to be perfect, just a lot better than any internal leakage to earth ground from house wiring or anything powered by that wiring.

 

Ok,but why does electricity try to go to ground into soil, gravel, stones,sand etc they are **** poor conductors and how does it return to its source ?

The earth is not such a poor conductor as you say. It is even used to carry current for long distance power transmission.