How a electricty works and why ?

Electricity is the 'flow of electrons' down a conducting wire. 

Like water, that flow can be under high pressure , high voltage. It can pass through in large quantities, high amperage.  Or it can be subject to resistance, like a water tap/faucet/valve. 

The difference in  'pressure down the conducting wire, is called Potential Difference and is measured in Volts.(V).

When you have a high amperage a lot of electrons are passing through a given point at once. This gives rise to heat in the wire/electric heaters.

When you change from a small flow under high pressure/voltage to large flow under low pressure, this is a TRANSFORMATION of electricity. 

Finally, Ohm's Law. Volts(V) equals Amps(I) times Resistance(R) 

Algebraically V = IR. 

Hope that helps!!!!