The chakras direct our life force to fulfill specific functions. Energy bodies are composed of energy that is subtler than our physical body. The sound of a mantra has a vibration designed to produce a specific effect. By attuning to this vibration when we meditate on a particular mantra, that effect is produced in our lives. Although mantra is an Indian word, these words of power have been used in the mystical practices of almost all cultures.
Optimum results come from daily practice - once or twice daily.
However, you may choose to meditate on an as-needed basis. If you are just beginning meditation and wish to practice regularly, it's best to start meditating 10 to 15 minutes once a day. After a while, you may want to increase that to 20 minutes once a day, or 10 minutes twice a day. More meditation is not necessarily better. Meditation taps into some very powerful inner energies.