At some places we generally see 3 lines in power supply where as in some other we see 5 lines. Can anybody please explain the difference?

3 usually means two circuit conductors plus a ground (earth).

5 can mean 4 are two circuits, plus one ground.

There may be other combinations, one is usually a ground.

You didn't mention in which country you saw this as well as the type & voltage of power system in use. In BS-LT-3phases,1neutral,1return for street light(total 5) or 1phase,1neutral,1 return (total 3). Earth or ground wire depends on type of earthing -IT,TT,TNCS etc. In HV 3phases & 1 earth wire(total4). I belief in USA/Canada-LT-220/110V-2phases,1neutral(total 3) or 3phases 480V,1neutral etc