Question

water does not spill out from a straw if you close its one end with your finger?

Answer 1

The water will not spill from the bottom as air cannot enter the top and, the Adhesive property between the water and the Cohesive property of the straw, prevent the water from flowing out. Also, the weight of water tending to push downwards causes a slight vacuum beneath the finger. The higher pressure of the atmosphere acting under the water, will also help to hold the water up. 
The moment you release your finger from the end, the air will push the water out as it enters.