Galvanizing is the process of applying a coat of zinc on to a steel surface.  Galvanizing protects the steel from corrosion.  Galvanizing is a very popular method of protection. 

The layer of zinc protects the steel from the environment.  In addition, galvanizing also provides galvanic protection. 

Galvanic Corrosion
Galvanic corrosion when two different metals are joined together.  When placed in a conductive environment, one of the metals becomes the anode while the other metal becomes the cathode.  The anode corrodes and is deposited in the cathode.  The anode thus wears off.

In galvanized steel, the zinc becomes the anode and wears off.  The steel is thus protected.

The coating can be of different thickness depending on the application.  Different surface finishes can also be made.

There are different methods of galvanizing

Hot Dip Galvanizing
Hot dip Galavanizing involves immersing a steel component in a molten bath of zinc.  A coat of zinc is applied to the component.

Electrogalvanizing involves electroplating a layer of zinc on a steel component. Zinc is connected to a positive terminal of a DC power source while Steel is connected to the negative terminal of the source.  Zinc gets deposited on the cathode.