Question

what is the significance of einsteins famous equation E=mc2

Answer 1

it is the formula Einstein derived from making the atomic bomb.

Answer 2

The formula didn't originate with the making of the atomic bomb, it is a consequence of Einstein's 1905 special theory of relativity.
You might think of it as one of the great unifications in physics. Before E=mc2, mass was mass and energy was energy, they were thought of as quite separate aspects of nature. After E=mc2 it was clear that mass and energy were intimately related - mass is a form of energy, energy has mass.
The formula tells you how much energy E is equivalent to a given mass m. The conversion factor is c squared, where c is the speed of light.
A little bit of mass converts into a lot of energy - c squared is 9x10^16.

Some years later the formula was applied in determining the energy release in the detonation of an atomic bomb.