While anyone can give Reiki and there are many ways to "heal" using Ki other than Reiki, the practice of giving Reiki cannot be learned from a book. Attunement into Reiki is a physical and energetic transmission that must be passed to the student from a Reiki Master Teacher.
Learning Reiki is a wonderful experience. Whether you are interested so you can use it on yourself and loved ones, because you are interested in becoming a Reiki practitioner or teacher, or because you are attracted to one of the many sub-branches of Reiki that have appeared recent years, all Reiki training should start with Level 1 training in a practice called Usui Shiki Ryoho (Usui's Healing Method), the original form of Reiki to be brought to the West by Mrs Hawayo Takata.
Traditional Usui Shiki Ryoho has three levels, although today the third level is split into a lower and upper level (Level 3A and 3B) taught as a series of 1 - 2 day workshops. Students are encouraged to proceed through the levels at their own rate but not to rush through them so as to attain Level 4 as quickly as possible For many people the first two levels are all that is required. Each level has its own qualities to be explored and techniques to be practiced. Once a student has received an attunement for Reiki at each level this alignment can never be lost or taken away; it remains a permanent alignment for the rest of the person's life.