okay basically there is pressure everywhere. pressure is pushing down on the water in the glass, pressure is pushing inside and outside the straw, etc. When you suck on the straw, you are reducing the air pressure inside of the straw, and to balance out this pressure from the pressure pushing on the liquid in the glass, water comes up in the straw. If there is a hole in the straw, the water wil not come up because the pressure balances itself out with the hole.
your mouth creates a vaccuum ( lesser pressure ) and the pressure ( from the atmoshere, greater pressure )on the fluid then pushes the fluid upward into your mouth
The water comes through the straw by suction you create with your mouth. when you suck on the straw, you decrease the pressure at the top of the straw. Fluids go from an area of high pressure to an area of low pressure so the water rises up the straw. When there is a hole poked in the straw, you cannot create the pressure gradient needed and therefore, the water does not come up the straw.
A straw works like this,as you take in the liquid
the in -take pressure causes the liquid to rise.If there is a hole in the straw it causes pressure loss.It won't work as well.