Why is electrolysis important?
Electrolysis is a process by which electrical energy is used to produce a chemical change. Perhaps the most familiar example of electrolysis is the decomposition of water into hydrogen and oxygen by means of an electric current.
But you want to know more about applications?
For example, aluminum is a very important metal. You can't get aluminum out of aluminum oxide just by heating the compound.
Aluminum oxide forms ions of aluminum and oxygen. Pure aluminum metal is obtained at the cathode, while oxygen gas bubbles off at the anode.
Electrolysis can be used for purposes other than preparing elements. One example is the refining of copper.
Also, another important use of electrolytic cells is in the electroplating of silver, gold, chromium, .... Electroplating produces a very thin coating of these metals on the surfaces of (cheaper) metals, giving them the appearance and the chemical resistance of the first ones.