1. Let’s start from mouth
Mouth + Food = Food Body or Physical Body or Annamaya Kosha. A baby when in womb develops this Body through its mother with the connection of ‘umbilical cord’ and later on when out of womb, the layer upon layer upon layer keeps on coming as the years go by, whatever he or she takes is just through the mouth or if in hospital is feeded by nurses or doctors through the veins. The physical body is composed of gross elements whatever we eat, it affects, builds or destroys our body. We owe this body to mother earth, father sky (ether), and other sisters and brothers: water, fire, wood, air. In a line, this body is made up of gross elements that are decaying.
2. Passages of body + Limbs = Vital body or Pranamaya Kosha. It also grows stronger or weaker in proportion to Food Body and Mental Body. And it grows stronger with clear mind and intellect and with healthy Food Body. Moderate Pranayama and Physical Exercise are good for it.
The Ego is a serpent which has two tongues: “This” and “I”.
3. This + 5 Senses = Mind or Sheath of Mind or Manomaya Kosha. All of its tendencies are outgoing, it is autostart and no auto-stop (it only stops when — a. it is absorbed in the object, b. when we witness it, c. when we seek its source, d. when we control it by watching breaths, e. when our understanding regarding it is deep, f. in deep sleep). By nature it is addictive and intense to addiction: touch, sound, color, taste and smell, these are the 5 senses and it is ‘mad’ for them or for their combination, as they exist outside, it is hard for a beginner to control the mind.
The mind is nothing but the bundle of thoughts made on the objects of 5 senses. It is as transient as the Food Body.
4. I + 5 Senses = Intellect or Sheath of Intellect or Gyanmaya Kosha. It is our CPU, where we store information, process, analyse and reach to a decision. It works according to the stored information, true information makes it shine and false information hangs it just before starting or at the time of processing. The predispositions and beliefs system (tested or untested) are its production and it shapes its reality by them. It feeds on accumulated information and nothing else.
5. The Last Sheath = The mind in sleep (without dream) turns ignorant to it, mind doesn’t know what is happening and so mind is not working. This ignorant state is called — Bliss or Sheath of Bliss or Anandamaya Kosha. Some advice to be in this body to gain pleasure but the sages say that it is just the sheath and nothing else and no wisdom is gained in it.
The above five bodies are mentioned in Upanishads, and each of them is transient, they feed on externalities, self-realization is nothing but to recognise the “Self” (or say, Atman, Brahman, Spirit, or Soul) is not these transient bodies.