Question

i cant understand what surface tension is exactly, plz tell me?

Answer 1

surface tension is a phenomenon in which the surface of a liquid, where the liquid is in contact with gas acts like a thin elastic sheet

Answer 2

The liquid molecules which are below the surface are in equilibrium.  The liquid molecules which are at the surface are attracted by other molecules in downward direction. So, a force is originated to balance the surface molecules which is equal but opposite in direction to the downward force. This force is called surface tension.