I've been using different power supplies for 6 years. But, I'm unable to understand how we make ground in a Power supply? Or from where does this ground come? Or from where does this reference ground come? Is it reference to earth or what?
As was clearly stated by EM Fields, "ground" is the reference against which voltages are measured against. Furthermore, in an isolated electrical system, such as a battery powered circuit, one might tie the positive terminal to "ground" and then all voltages measured against "ground" will be negative. Ground is simply a reference, nothing more.
Back in the stony ages when relays were first used for telegraphy, it was found that instead of making a circuit by running two copper lines from station to station, in some locations a long rod could be driven into the earth at each station and the earth between the rods used as one of the conductors, eliminating the cost of one copper wire.
Then, because Benjamin Franklin told everybody that electricity moved out from the arbitrarily named "positive" terminal of a battery and returned to the negative terminal, the batteries used to run the relays at telegraph stations were connected with the battery's switched positive terminal connected to the long copper lines stretched between stations, and the return connected to the ground terminal.
The term stuck, and as time went by and circuits got more complicated, all of the components returning current directly to the battery's negative terminal were said to be connected to "ground", or "grounded".
Thus, "ground" became a reference against which voltages in the circuit were measured and, today, has come to mean the common point which all galvanically interconnected equipment shares, whether or not a direct connection to the Earth is made.
Earth serves as a (reasonably) constant potential reference against which other potentials can be measured.
The use of the term ground (or earth) is so common in electrical and electronics applications that circuits in portable electronic devices such as cell phones and media players as well as circuits in vehicles may be spoken of as having a "ground" connection without any actual connection to the Earth. This is usually a large conductor attached to one side of the power supply (such as the "ground plane" on a printed circuit board) which serves as the common return path for current from many different components in the circuit.