The wings are pointed towards the wing tips because most of the aircraft flying today use swept wings.
The swept wing, where the wing is swept or the wing chord reduces towards the wingtip is to reduce the wave drag. This is mainly seen in the aircraft flying in transonic (civil airliners) and supersonic (combat aircraft), while rectangular wings are used in low speed general aviation aircraft.
Sweeping the wing has the effect of reducing the normal velocity of the airflow as seen by the wing, by the cosine of the angle of sweep.
Source: history.nasa.gov
This has the effect of increasing the critical Mach number, above which the wave drag increases significantly.
Source: history.nasa.gov
Some rectangular wing tips are rounded off for the same reason- to reduce drag, though in this case ,they are there to reduce induce drag.
Source: Sport Aviation
However, the effect is marginal, so quite a few aircraftsaircraft go without it.
Source: Sport Aviation
Another reason for airliner wings becoming 'pointed' towards the tip is structural- The wing is practically like a cantilever beam, and reducing the cross section (of the large and long wings) towards the tip reduces the root end bending moments.
