Energy is a type of matter that is present in every ounce of reality at varying amounts. This energy isn't detectable by most traditional scientific instruments, though it is detectable directly by life forms, as well as the life forms being able to manipulate this energy as well. This "Energy" is unique in the sense that while it comes in many predefined forms very much similarly to physical elements, it can be twisted and changed without much issue.
Every living form (and some non-living) have a thing called an "Energy System". This is a system that allows the organism to manipulate the energy for whichever purpose they so desire. (Something of note, lower energy = more negative effects, so if it was completely drained of it's energy the life form would likely die). This system is layered into the physical body of the organism, though it isn't directly viewable in it. (I personally am of the belief that energy is the "fourth dimension" hence why it is so hard to measure with our current instruments.).
It is of note though that the system is made up of many parts, firstly pathways. Pathways more energy throughout the body, there are often main ones going down each limb and secondary ones branching off of those. At the intersection of main pathways there is "Chakras". These are energy centers and where many important functions are carried out. Finally, at the end of each pathway there is a Nadi or Energy Point. This is where energy can be outputted and inputted.