Prana (using the Yogic Science model) is yet another description of the indescribeable. It is said that it is what animates all life. In the human organism it enters through the medium of breath; through the Nadis and the Energy Centers. It is similiar to the TCM view of "Chi" or "Qi". Prana permeates the universe. All disease is said to be related to some imbalance with this subtle energy. Obstructed flow or stagnation and other states in which prana doesnt flow properly (harmoniously) through the organism are examples of states of imbalance.
In Yogic Science, one approach to harmonizing the body with prana is to practice Hatha Yoga, using Asana (special postures for the body) and Pranayama (Breath excercises) on starts to loosen and release blockages of pranic flow.
In TCM, adjusting Chi flow flow can be done through physical practices (internal alchemy) for example: Tai-Chi, Chi-Gung etc...
Medicinally, it can be done through Accupuncture, Moxybustion, Accupressure etc...
This is a superficial description of what prana appears (to be).
Related: Energy, Yogic Science