Bernoulli's theorem states that the mechanical energy of a flowing fluid remains constant. There are 3 components in the mechanical energy - the potential energy, the kinetic energy and the energy associated with fluid pressure.

This can be seen in multiple places.

In a water park, as the water comes down a slide it loses potential energy and gains kinetic energy.

When water flows through a horizontal channel with varying widths - when the channel is narrow, it flows fast and when the channel is wide, it flows slowly.

According to Bernoulli's theorem as the channel becomes narrow the energy associated with fluid pressure decreases, the kinetic energy increases and the potential energy remains the same. The decrease in energy associated with fluid pressure equals the increase in kinetic energy.