Reiki is a Japanese technique that is used for relaxation, healing, and the movement and flow of energy. The word Reiki: Rei (God, Source, Universe or Higher Power) and Ki (life force energy)--so the life force energy that moves through all things created by Source. It is based on the idea that everything and everyone is connected to this life force energy and it can be used for healing by the laying on of hands. I feel that everyone (since all are connected to the One Source) has the ability to generate and use Reiki. However, formally, a Master gives "attunements" to connect one a bit deeper to the energy to be able to guide the energy to its highest place. Reiki (as well as most other energetic modalities) can be sent at a distance. It moves beyond our normal physical confines and with intention can still affect an individual no matter where they are in the world!
A client in person or at a distance would just need to lay comfortable and focus on their breathing. Holding their intentions for their healing, and the energy will do the rest. It goes exactly where it needs to to provide the optimum affect for the individual.
In my Reiki sessions, I often implement the use of crystals to lay on each chakra. Affects of the energy could be immediate or latent and can vary. Overall, the clearing of what no longer serves energetically leaves one freer emotionally and physically: relaxed, rejuvenated and renewed.