There are many books on this site that can help, along with help people on the site.meditation is a first step..like mentioned before. You might be able to start picking up on people's atmosphere...and focus on the people and you will be able to see their colors. A lot if practice
I will try to put this into this thread instead of messaging you, the references will be as helpful.
Let's begin with being able to sense / see auras. There happen to some exercises to develop the skill of sensing / seeing auras. Your aura is basically the electromagnetic field of energy which is externally surrounding your body and forming your personal "energy space". This is a natural thing, and also the ability to see / sense it is nothing extraordinary or impossible.
Everything depends on how you are familiarizing yourself with aspects of energy, and the proper psychic development needed in order to achieve the ability to successfully sense or see the auras surrounding specific objects.
That is a recommended article about the very basic forms of aura seeing
Later, after you get into some techniques of seeing auras, practice for some period and develop your skills. I'd personally advice you to take the next step and learn to do what's called "reading" the auras you see. You may find this article as very informative and helpful for this:
This one specifically focuses on reading the auras:
Since you asked about cleansing your aura, I'll recommend you a good article I found here on this site