The video below is an excellent walk-through of how a refrigeration cycle works.
The video features a system that uses sight glass instead of copper piping, allowing the narrator to show the inner workings of a heat pump system. You will see the refrigerant itself as it evaporates in the pipes, slowly changing from liquid to gas, absorbing heat as it does so.
The narrator is very knowledgeable and I’m sure you’ll learn a thing or two, even if you’ve been working on HVAC systems for a while.