The main (central) sets of 7 chakras form a fractal system, with an infinite set of similar ones (both upwards and downwards) but less and less significant the further away they are from the main set.
The chakras are larger in extent than I’ve illustrated here when in good condition, and each chakra has a pair of components one of which spins clockwise, one of which spins anti-clockwise.
The chakras are in part a form of energy-transformer, supplying different frequencies of energies to the meridian-system and other body-systems. Other functions include communication and awareness at their range of frequencies.
The main set of chakras (i.e. chakras for meat-body) has 7 chakras. The lowest is red and is about physical survival, material existence etc. The second up is orange, and is about sex and reproduction. The third is yellow and is about power. The 4th up is green and is bout connections with other things. The 5th is turquoise and is about communication. The 6th is blue and is about awareness, and the top one is indigo and is about connection with higher things (“spirituality” etc.).
As on the illustration, above the main set is another set of 7, which are the chakras for the Etheric-double. Some belief systems mistakenly see the first one of those as an 8th one of the main system. Below the main chakra set is another set for the Astral-body. These sets other than the main set are not really the colors I’ve illustrated (and the main ones only relate harmonically to the illustrated colors, as they are not in the Physical-universe Playing-field), but are something like related harmonics of those colors.
Reiki and Hatha-Yoga work on the chakras, but traditionally only on the main set. In addition to the sets of 7 chakras which are on the vertical energy-line (which is infinite both upwards and downwards and is where some of the energy transformed by the chakras mainly comes from), there are many other chakras (some of which are illustrated here). The main additional ones are on the joints, and these are worked with in Reiki, plus there are series’ of chakras extending out from each limb (as illustrated). The knee chakras (and the chakras in the series below each knee-chakra) are particularly important for the power of the Kundalini and other body-systems. The chakras in a line up the legs, are on a line of flow, from below the legs, up to hips and then the flow joins and adds to the upward flow of the main sets of chakras. The same applies to the chakra-sets along the arms. These flows should be clean and powerful, if in good condition.
The main sets of chakras have input from behind the body, and output towards the front (in addition to their connection to the infinite vertical energy-line). This flow can be cleaned somewhat by temporarily reversing it for a few seconds, then putting it back to normal. The additional chakra-systems outside the 3 ones labeled here, have each set connecting somewhat to a chakra in the main sets.
Some versions of Hatha Yoga suggest a particular symbol for each chakra. While these symbols can be of use initially to help clean and focus the energy of each chakra, one should not use them beyond that point, as they are too narrowly focused, and not precisely correct for the perfect operation of the chakras. The reason the Chakras come in sets of seven is that the Heart-Chakra is really at a slightly senior level compared to the 2 sets of 3 Chakras either side of it.
There is at least one additional Chakra with different properties to those illustrated, so could be considered either as a Chakra, or as a separate type of body-system (some Eastern traditions use the word “chakra” for any energy-formation, such as the Brains etc.). This is the KalaChakra (not illustrated), which has its origin behind and slightly below the Solar-plexus (its shape can extend upwards into wing-shaped formations, illustrated (inaccurately) in many traditions) which has various functions including creation of specific energies. In most humans on earth it is almost entirely dormant (which can often increase tension across the shoulders). None of the “KalaChakra” traditions on earth currently are working cleanly or directly with the real KalaChakra.