youngs double slit experiment please explain briefly

In YDSE two slits of equal width are cut with distance between them equal to d(it should be of the order of wavelength).

A screen is placed at a distance D from slits(D>>d).

Now the slits are illuminated by a source of monochromatic light.

Then we observe the fringe pattern on the screen with adjacent bright and dark fringes.

IMPORTANT FORMULA USED FOR CALCULATION ARE:

                                             1.   β=λD/d   ( β is fringe width)