The Earth is surrounded by a cover oi air called atmosphere. it extends to a hundred kilometers above sea level. Just as certain sea creature live an bottom of ocean. we live at the bottom of a huge ocean of air. Air is a mixture of gases. The density. of air in the atmosphere is not uniform. it decreases continuously as we go up. Atmospheric pressure acts in all directions.
Take an empty tin can with a lid. Open its cap and put some water inn Place it over flame. Wait till water begins to boil and the steam expels the air out of the can. Remove it from the flame. Close the can firmly by its cap. Now place the can under tap water. The can -wi|l squeeze due to atmospheric pressure.
When the can is cooled by tap water. the steam in it condenses. M W steam changes into water. it leaves an empty space behind it. This lowers pressure inside the can as compared to the atmospheric pressure outside the can. This will cause the can to collapse from all directions.
The fact can also be demonstrated by collapsing of art empty plastic when air is sucked out of it.