These 'Pascal Vases' as they are known may vary in design greatly although most comprise of around four glass tubes bent in different ways. One is usually straight and wider than the others - this is the one you pour water into. As you pour you will see the water entering the other tubes from the bottom. Given time to fill, the water level in all of the tubes should be equal.
You may want to add a small amount of food dye to the water to make it stand out and make the effect more visible.
This equipment shows that the pressure in the bottom of a fluid depends of the depth of the liquid and not the shape of the container. Because atmospheric pressure equal on the surface of the fluids in all of the tubes, the fluid levels in each should be the same.