The first thing I would like to explain to you is that you cannot “understand” the world of the unseen, but you can come to know it. Understanding is using your mind. Knowing is using your spirit.
Why would you want to get to know this “unseen” world? For two basic reasons. This world of spirit energy is all around you all of the time. It affects you. 
It is within this world that you create your reality. So knowing this world is knowing how to create a better life for yourself.
Knowing the unseen world outside of you is only half of the answer. First you need to know and be able to access the unseen world within you. The unseen world within you is your own internal energy that helps or blocks your dreams and creations. If you can master knowing and cleansing your internal world you can be successful, have good health, great relationships and give yourself the lifestyle of joy and happiness.
When people seek to know their energy or their spirit they often seek to study being psychic. However, psychic is just an umbrella term. Psychic covers many abilities that people are born with and can develop.
Psychic covers: Telekinesis; Clairsentience; Psychometry; Healing; In and Out of Body Use & Info; Clairaudience; Telepathy; Precognition, Inner Voice; Abstract Intuition; Clairvoyance; Mediumship; Channeling; & Knowingness.
Usually people study one “psychic” skill and get really capable with it. This in turn opens you to other skills and knowingness. Being psychic is just a footstep into the world of the Oneness. Often people who get really capable with a psychic skill think it is the end all but actually it is a rung on the ladder to the Oneness of Enlightenment which is the connection to the whole. It is therefore just one of the doors to the higher levels of awareness.