@swati In Physics, Interference is the interaction of two similar waves. For example, if you throw two stones into a pond of still water at the same time, there will be two waves that will eventually cross each other. At each point one wave crosses the other, the point in the medium (water here) will have the net displacement from its mean position in accordance with the vector sum of the displacements for each wave. The point where two crests meet will result in double the individual crest. Where two troughs meet, will have double the individual troughs. Where One crest meets one trough, net displacement will be zero.
If you look carefully into the animation I have attached, you will see, that at a screen that is placed equally distant to the centres of both the waves, an alternating maximum, zero, and minimum pattern is created. When we apply this concept of interference pattern to light waves, or any electromagnetic wave, we get the same result with a slight modification. With electromagnetic waves, on the screen, we get intensity patterns. Since the intensity of a wave is directly proportional to the square of the amplitude of the wave, the maxima and minima result in the same intensity. Remember that minima are the negative maxima and the square of -1 is just 1. Thus for EM waves, interference produces bright (max or min) and dark (zero displacement) patterns. We call these fringes.
NOTE: For interference of two waves to produce fringes, they must be of the same frequency (or wavelength), else, the pattern will not be constant and won't be clearly visible.