This is going to be hard to explain without pictures, but not impossible.
In Asian medicine and philosophy, such as acupressure, acupuncture, shiatsu, reiki, herbal medicine, yoga the thinking involves a system of lines of energy (energy being called chi or qi). The lines are called meridians, and are related to various organs. The idea is to keep the energy balanced like the yin/yang symbol that is so fashionable amongst "hippies" and "surfers" etc. Balanced means not too active (fast) or passive (slow or stagnant), hot or cold, yin or yang. There are points along meridian lines called meridian points.
In both Indian and Chinese medical thinking, there are major centres in the body called chakras. Common examples that people are often aware of are the "third eye" (between the eyes on the forehead), which is where you picture things in your mind, and the solar plexus (just above the belly button) which is your centre where you are taught to focus your energy from in martial arts or the healing arts. However, there are a few chakras along the spine/centre of the body. They are whirls of energy (chi) that, when healthy, open out to the back and front of the body. Each chakra is associated with the glands that are in its area.
Although some of the concepts may seem unusual to anyone fresh to them, think about where you feel things in your body and where reactions and activity happen, use your observational skills, and you may find correlations. Everyone is unique, and experience, observation, reflection and application are the best teachers.
Here is a list of chakras starting from the top of the head. There are slight variations in different schools of thought.
The one at the top of your head is called your crown chakra in English or "Sahasrara". It is associated with integration. It manifests as cool vibrations. It's where the higher order, cosmos, "God", your higher Self connects and communicates with your humble earthly self. It is clear light.
The one called your "third eye", already described, is also known as "Agnya". It is associated with forgiveness. It manifests as sight, hearing, thought and a sense of "I". It is where inspiration and vision is seated. Its colour is purple or violet in some schools of thought.
The throat chakra, or "Vishuddhi", is your communication and expression chakra. It is located in the throat near the bottom of your neck. It is associated with diplomacy, collectivity, and the witness state. It manifests anything to do with the face, mouth, tongue, neck or arms. In some schools it's colour is blue.
The heart chakra is on your spine at heart level. It is associated with love and compassion. It manifests in the heartbeat and breathing. In some schools its colour is green or pink.
The next one down is the solar plexus or "Nabhi", already described. It is associated with peace, satisfaction, and well being. It is your energetic core, where your strength and personal power is seated. It manifests in the working of the stomach and liver. It's colour is yellow (like the sun).
There is another chakra that surrounds the solar plexus called the void. It is associated with self-mastery and manifests in the liver, kidney, spleen, pancreas and uterus. Uncertain of its associated colour, but suspect it's green.
The sacral chakra or "swadisthana" is located above the pubic bone where the womb is in women. It is associated with abstract thought, creativity, aesthetics and sexuality. It manifests in the same things as the void. Its colour is orange.
The lowest official chakra is the base chakra or "mooladhara". It is located at the base of the groin. It is associated with innocence and wisdom. It manifests in reproduction and elimination. It is a source of primal, earthy, animal energy. Its colour is red.
Just above the base chakra is the seat of the kundalini, located at the sacrum bones. It manifests in the parasympathetic system. It is associated with motherly love.
The colours represent different energy or light vibrations which inspire different emotional responses. Here is what they are generally associated with. Like a rainbow, the high vibration (more spiritual) colours are at the top, and , as the vibration gets slower and lower (more earthy, physical and manifest) they are lower down on the rainbow.
White is pure or raw light, containing all colours.
Purple/violet is high vibration spirituality.
Blue is expression and communication.
Green is healing and growth.
Pink is unconditional or pure love.
Yellow is personal strength and power.
Orange is creativity and sexuality.
Red is primal energy, passion.
The kundalini is the energy that is used in tantric (tantra being a form of sexual meditative practice) schools of thought. The medical symbol of a sword with a snake or snakes wound along it is a representation of the kundalini (snake) rising up through the chakras along the spine (sword). The kundalini is seated in the region where the sacral bones are (back of hip), and is a primal, sexual, energy source referred to as a snake, or the "goddess" or the Mother. In tantra the loins of a woman is often referred to as the "gateway to the heavenly palace". When the kundalini is awakened (this can happen through spiritual awakening and meditation or through a traumatic event), it can rise up the spine, through the chakras (activating them with the primal energy of the kundalini), to raise and activate the soul into the higher vibrations. However, because it is such a strong raw energy that can be destructive as well as creative, one should be careful and healthy when one is playing with it's energy. If there are blocks in the chakras or the kundalini gets "stuck" it can be unpleasant to put it mildly. However, with expert guidance and experience, it is a very potent and wonderful area of Life to explore, understand and utilise.
If you want to find out more - and there is a lot more - just google the key words, pop into your local new age book store, yoga class or alternative health practitioner with an eastern influence.