Many people believe that there is a life force energy that permeates our bodies. Our bodies use this energy for maintaining itself or for healing itself from injuries or illness. When there is a shortage or blockage of this energy our bodies become ill, possibly resulting in death. It is also believed that there is an unlimited supply of this energy available in the universe. Usui Sensei supposedly learned how to channel this energy from the universe through his body and into people who were ill. When someone who is ill receives this energy, it can accelerate the natural healing process. There are many reports of miracle type results from this process.
Usui Sensei was able to teach others how to transfer this energy, making them Reiki practitioners. As a Reiki practitioner, one can transfer the Reiki energy into another person by laying-on of hands, even from a distance. Usui Sensei was also able to teach practitioners how to teach others, making the practitioners Reiki teachers. Once someone is a Reiki teacher he can make other Reiki teachers, thus carrying on the tradition. A teacher does this by opening up an energy channel in the practitioner, from the top of the head to the hands. This enables the Reiki energy to be channeled from the Universe through the top of the head and into the hands. This process is called an "attunement." To channel Reiki energy you must have had an attunement by a legitimate Reiki teacher. Once a person has had an attunement they are then able to channel the energy through their hands and into other people.
In the Reiki system taught by Mrs. Takata, there are 3 stages or degrees a practitioner must go through before becoming a teacher. In the first degree a practitioner receives the initial attunement which enables them to channel Reiki energy for physical healing. In the second degree an additional attunement is given which enables the practitioner to channel Reiki energy for emotional healing and protection, and to perform healing from a distance. In the third degree the final attunement is given which enables the practitioner to channel Reiki energy for spiritual healing and for opening up the Reiki channel in another person.
The two characters above are "Rei-ki" written in Japanese. Rei in Japanese means spirit. And ki means life force energy. Together they can be read as "spirit led life force energy".