Namaste, Arin!
Thank you for your interest, and I wish you much luck on your journey!
You can learn more about Reiki on these topics:
Energy Medicine by Mohan
Learn about Life Force energy here and the many names for it, what energy healing is, and what it does.
What Is Reiki by Mohan
Learn what exactly Reiki is and how it is used.
The Usui Reiki Shiki Ryoho Gakkai (Traditional Reiki Methods & Techniques) by Black_Ki
Some additional information on Reiki.
Causes of Illness by Black_Ki
Black_Ki does a marvelous job of describing a list of problems and their cause!
Reiki is chi/Ki that is channeled from around us and from the Divine and sent through us for healing. Attunements are used to open us up to channel Reiki and increase our vibration to closer to the vibration of the energy. The more and higher vibratory Reiki we use, the more powerful our healings become and the more peaceful people we become, because giving a Reiki healing to someone else is also a Reiki healing for us.
Usui Reiki is given in three attunements: 1, 2, and Master. Level 1 allows us to channel the Reiki through us.
Level 2 allows us to use the three Sacred Symbols.
Master Level allows us to use the Master symbol and attune others.
Kundalini was created in addition to Usui Reiki. Kundalini allows Reiki to flow up from our Root chakra and gain access to the earth's beautiful energies. When one becomes attuned to Usui Reiki Master, he may then be attuned to Kundalini level 1. Level 2 builds upon the last, and Kundalini Master level builds upon the last.
If he wishes to continue expanding his Reiki channel, there are 6 Kundalini "boosters" which are like mini attunements.
Ethereal Crystals Reiki attuned us to many different crystal energies to use in healings and comes in levels from 3 to 12 depending on the system being used.
And there are many more!
I hope this has helped and blessed you.
Highest blessings!
-Wes