When we pour chilled drink in the glass or other utensil then the liquid condenses on the outside of that glass.Why this happens & from where that liquid comes ? Is that liquid water or something else ?

This is moisture from the surrounding air that collects on the outside of the glass. The more humid it is outside, the quicker the moisture on the outside of the glass will form. Such as a hot, humid summer day and a cold glass of water with ice in it will form the moisture on the outside of a glass very quickly.

twinkiedooter is right. Plus the difference between the temperature of the glass and the air temperature will also determine how much water condenses. Any cold surface exposed to humid air will cause water to condense out of the air. If the surface is absorbent, like a fabric couch or a wood surface, it will absorb the water and you won't see it. But on glass or smooth metal it's really obvious.