Q: What is 'energy work'?
A: This is difficult to explain in just a few sentences, and specific interpretations are debated even among long-time practitioners, as well as scientists. However, simply put, if we understand that our bodies are comprised of some life force, which in this case we'll call 'energy', then we can also understand that any disruption in this energy might cause disruptions in our bodies.
So energy 'work', which is also called energy 'therapy', or energy 'healing', is designed to assist in returning our bodies to their natural energetic patterns. For example, if a body is experiencing a headache, one could interpret this as a blockage in the flow of energy, though not necessarily in the head region. So energy therapy would attempt to restore the natural flow of energy to that particular area, or if necessary, to the whole energetic system, so that the headache is relieved.
For a more in-depth understanding of energy work, I recommend first learning more about our bodies' energetic systems, and about the life force we're calling 'energy' which is referred to in different cultures as ki, chi, prana, etc. By first understanding this life force, we can then understand how to 'work' with it in terms of our well-being.