Your Thoughts and Feelings Emit Energy
Energy is everywhere - the typical human picks up a certain spectrum of energy and there are some whose sensitivity extends beyond that spectrum, either innately or by training.  For some psychic, seeing auras is a natural part of their range of perception.  Using their intuition to interpret it.  Your aura is an egg-shaped energy field encompassing your physical body. 

It has seven layers.  The layers closest to the body relate to physical aspects like health, the mind and your emotions while the outer layers are to do with your spirit.  There is much in the aura to read.  Some psychics use the ever-changing array of colours projected by your health, thoughts, emotions, moods hopes, fears and more.  Each colour has many shades and each shade has a different meaning, so it's not just a simple case of "red means passion".
How to See Auras

• Choose low, indirect light and a pale, plain wall behind you.
• Sit facing a mirror and let your gaze focus beyond your image.
• Eventually you will see a glow/haze - the aura!
• Try this with objects, animals and people.  
• As everything - people, thoughts, spirit - is energy, you'll come to see how your own aura interacts with all of life.