"Happiness is a sort of action"
Aristotle

A Reiki healing is a great example of letting everything be as it is, of doing by not doing but just simply being there, of going with the flow.
One of the truths of Reiki namely is, that the healee - not the healer - decides the amount of needed energy and for what aim this energy will be used. The healer is a channel, a facilitator who passes on positive energy, but the healer is never the one who actually does the healing; that is an interplay between the healee and universal life-energy. The free will of the person who receives healing decides to which level healing will take place and the Reiki energy will do the work. The task of the healer is to have the intent to let healing or improvement take place and to passively allow the energy to flow through the healer's hands to the healee. In short: the one who needs healing somehow decides "I want to receive", the Reiki practitioner somehow decides "I want to give" and this connection in openness and love is enough to let the Reiki flow. Most of the time Reiki will be experienced as warmth or heat, as if a blanket of loving attention is put over you. But other sensations like coldness, tingling, prickling, throbbing, shivering, emotional release, memories popping up or no sensation at all are possible too. Giving Reiki often fills the healer with happiness, gratitude and humbleness. Receiving Reiki often fills the healee with happiness, peace and relaxation. And in the restoration of inner balance and calmness healing automatically takes place.

There are two main ways of giving Reiki: Hands-on healing with a physical present person-animal-plant, or
Hands-off healing (distance healing) where the person receiving healing does not need to be present in the same room. Both methods will be described below.

Hands-on healing

Here Reiki is practiced in the form of simple touch-healing.
The most convenient way is with the client lying down on a massage-table, bed or mattress on the ground. If not possible a sitting position or any other position of course is possible too. It is important to know that Reiki will be given clothed; you only need to take your shoes off so that your feet can be treated too. If ever you meet a practitioner who states that you need to take off your clothes for a Reiki session: immediately leave the room without paying! The practitioner will put his/her hands on you without exercising pressure and without making massage movements. An intuitive healer will first move his hands through your energy field to sense which areas need healing and place his hands there afterwards; a less intuitive or more organized working person will use the standard hand positions which cover all important areas of the body. Both methods work equally well; remember that the Reiki energy travels anyway to the places where it is needed. Each hand position will be held between 3-5 minutes average, or longer when needed. An indication is given by the sensations the practitioner feels in his hands, or by his intuition and/or inner voice. Usually a full body treatment takes about an hour.

The so-called 'personal areas' meaning sexual areas: breasts, buttocks and genitals usually are not treated hands-on. On these body-parts most healers work in the aura several centimeters above these places. The reason behind this is the fact that many persons live in a sexual distorted world, have experiences with sexual abuse, or are brought up so touch starved that they immediately connect touch here with sexuality, which often is not promoting feelings of trust and safety. And of course you wish to feel safe during a healing. A good guideline is this: if you have physical complaints concerning the breasts or genital area it needs to be discussed before the treatment if you will be touched there; if not you will be treated in the surroundings of these places or in the aura above them. If the practitioner is someone you know well (a friend or partner) then it is often easier to be touched on these places; still I advice to ask on beforehand to not disturb people's feelings of security. Reiki is no massage; the healer will hold his hands still on one place before moving on to another area.

Reiki touch-healing can be practiced on humans, animals, plants, minerals and even inanimate things. The last thing may seem unbelievable, but it has been reported that cars with empty tanks drove on when Reiki was applied. This does not always work; to me it especially seems to work in emergency cases. Usually it takes less than an hour to treat children, animals, minerals or plants. You can charge sigils, amulets, talismans and gemstones this way. Or improve your food, drinks, medicines, etc. just by holding your hands around or just above it for a while.
In hands-on healing you can make use of the Reiki symbols to consciously focus on a certain beam of the energy, but you can as well heal without the symbols.

Distance healing

If you're not acquainted with this it is a weird thing that you can treat someone or something not being actually present. And it is really great to experience that it is possible. Time and place belong to the third dimension, but Reiki goes so much further. If you would want you could heal someone on Venus for instance. Why should we want to use distance healing? First of all for beings who cannot be physically with you, like a far away living family member. Second for beings who cannot sit or lie still for a treatment, like children and animals. Third for body-parts which hurt too much to be touched, like burns. Fourth it is a convenient way to treat yourself (putting your hands on your back for instance is not really comfortable). And a very interesting option: you can send energy to a situation. You can explain the universe a certain situation in the present or the future (for instance an appliance or a test you have to make) you wish to influence in a positive way, and after having declared your intention send Reiki to it. You can also declare your (detailed) wish to make something appear in our physical reality and send Reiki to it. These are forms of magick.

In distance healing we make use of something to represent the one the healing is meant for (a proxy), like a photograph, address, doll or teddy-bear we declare represents that person in that moment. Another well known method is projecting someone or something on your upper leg; in this case the knee represents the head of the person, the upper thigh the legs and feet of the person and everything in between represent the body-parts in between of the person or situation you treat. I know it sounds weird and unbelievable, but thousands of people work this way with great results. It has for instance helped me make further kidney dialyses unnecessary for a person I only know by email. In distance healing we must make use of the symbols; the number of symbols is variable but at least you need the power symbol and distance symbol which travels through time and space.
Another possibility of distance working is adding Reiki symbols to your visualizations or to the positive, loving thoughts you send out to heal someone; the Reiki symbols will make your work more powerful

of course you can write down affirmations or your wish on a piece of paper accompanied by the Reiki symbols and hold it between your hands. Or you can use your hands to beam reiki-energy to both present or non-present persons by visualizing the symbols, placing your hands palms out towards the person or visualized person and intent healing.

Other forms of using Reiki

Usui taught that Reiki radiates all over the body of the healer, but especially through the hands, eyes and breath.
Healing with the eyes is not commonly done, but I'm sure you know how much love radiates from the eyes of a truly open and loving person. So if you are initiated in Reiki you can consciously use your eyes to beam loving energy with.
Dr. Usui also used blowing the breath on a body-part which needs healing. Remember that the bible states that human forms were made of clay and that God blew them to life with his breath? Usually you don't learn this in a Reiki course and I suppose that has to do with our intimacy starved society. Reiki masters however do use the breath while doing attunements, and in Reiki Tera Mai (the Reiki branch of Kathleen Milner) blowing healing energy into a person is used again.
And please don't forget that the chakras in the soles of the feet get activated too with an initiation; not very applicable to treat a person but really useful to treat a pet that lies before you, just gently put your feet on them, they will love it.