The fact that liquids exert pressure can be demonstrates from the fact that if we have a liquid (say water) kept in a container then is we make an opening in it then the water will rush out through the hole with some speed. This is due to the fact that water exerts some pressure on the walls of the container.
This is a very simple way to show liquids exert pressure...
Let us take a big plastic mug.
Now, we can make holes anywhere on the container to demonstrate that pressure is exerted by liquid there.
We can make holes on sides at different heights
We can also make holes at the at the bottom of the mug
and anywhere else for that matter.
We would see a stream of water coming out of the mug making a parabola trajectory.