### Theory:

What are fluids?
All the substances that flow are called fluids. All liquids and gases come under the category of fluids.
Like, solids liquids also have definite weight, and they also exert pressure. When a fluid is filled in a container, the fluid exerts pressure in the walls of the container and also at all points of the fluid. Since the fluid molecules are in rapid motion, particles are likely to move randomly, equally in any direction. Therefore, the pressure exerted by the fluid acts in all directions. Pressure in fluids is calculated by using the below formula,

$\mathit{Fluid}\phantom{\rule{0.147em}{0ex}}\mathit{pressure}=\frac{\mathit{Total}\phantom{\rule{0.147em}{0ex}}\mathit{force}\phantom{\rule{0.147em}{0ex}}\mathit{exerted}\phantom{\rule{0.147em}{0ex}}\mathit{by}\phantom{\rule{0.147em}{0ex}}\mathit{the}\phantom{\rule{0.147em}{0ex}}\mathit{fluid}}{\mathit{Area}\phantom{\rule{0.147em}{0ex}}\mathit{over}\phantom{\rule{0.147em}{0ex}}\mathit{which}\phantom{\rule{0.147em}{0ex}}\mathit{the}\phantom{\rule{0.147em}{0ex}}\mathit{force}\phantom{\rule{0.147em}{0ex}}\mathit{is}\phantom{\rule{0.147em}{0ex}}\mathit{exerted}}=\frac{F}{A}$

The above picture shows that gases can be compressed.

First, we will discuss the pressure exerted by liquids, and then we will discuss the pressure exerted by the gases.

Pressure due to liquids:

The force exerted due to the pressure of a liquid on a body immersed in it and on the container walls is always perpendicular to the surface.

We can see the pressure acting on all sides of the vessel in the above diagram.

Balloon immersed in a tub of water

When an air-filled balloon is immersed inside the water, it immediately comes up and floats on the surface of the water. This shows that water or other liquid exerts pressure in the upward direction. Similarly, liquid pressure acts on lateral sides also. When a bottle with water is pierced on the sides, we can see water coming out with speed; this is because liquid exerts lateral pressure on the walls of the container.
Reference:
https://www.flickr.com/photos/121935927@N06/13580040284