Pressure is a scalar, physical quantity which is the ratio of force to the area over which that force is applied.The formula of pressure is as follows:
P = F/A
Earth is covered by air containing different gases which makes the atmospheric pressure of earth. The pressure of molecules acts on all bodies from all direction. Take a balloon for instance. If you were to blow air in a round balloon, it would swell in a perfect round shape as the air would put pressure on its insides from all directions. Hence, the balloon would take a perfect round shape.
Real Life Application of Atmospheric Pressure:
Atmospheric Pressure plays an important role in our daily lives as well. We drink juice from a box with the help of Atmospheric Pressure. The act of sucking through a straw creates a vacuum in the box as the air is sucked from it.
When you suck the air out of the straw, the drink in the box is pushed up by the air that is still on top of the drink. You use your mouth to reduce the pressure over the fluid inside the straw. The pressure over the rest of the liquid in the box continues to be exerted and, because it is higher than the pressure over the liquid inside the straw, the net effect is for the liquid to be forced from the area of higher pressure to the area of lower pressure.Hence, the drink goes in your mouth from the straw.
If you keep sucking even when the juice is finished, the box will get pressed inside. This happens because the action of sucking the air creates an area of lower atmospheric pressure in the box. Hence, the air outside which has a higher pressure applies the force on the box, thereby pressing it. Previously, the air inside the box had been exerting an equal pressure on it than the air outside the box. So the box had maintained its shape.