All websites about the occult mention non-human and non-physical entities. Many websites and books recommend working with entities and tell you how to do it. But the truth is, most famous types of entities don't actually exist, at least not the way people think they do. For example, if you cast a spell and mention the name of an entity to get help, the spell may work regardless of whether the entity is real or not. That is because trusting an entity makes your belief in the spell's success stronger which in turn makes the subconscious mind help with the process without you realising it. That is why people of many different traditions can cast spells successfully.
However just because most entities aren't real, doesn't mean there are no non-physical entities. There are actually many different kinds. The most common entities are the ones that were created by experienced spellcasters to perform tasks. They are created by energy and they feed on energy. As a result, they get stronger and become an independent entity. There are even many ancient entities called "gods" that were created that way. There are also entities that were not created using energies by humans. They exist on other planes like astral plane and they have evolved over time just like humans did. While most beginners want to work with entities, it is actually not a very practical decision. Using energies directly is usually a better idea than using entities that can control energies. That is because it is not very easy to create or call entities who will help you in exchange of something and they can also cause problems later. Until becoming very experienced with spellcasting, I don't recommend working with entities. I personally never work with them when I'm casting a spell for someone else but for some specific spells and for other purposes like gaining information, they can be quite useful.