Bija mantras are typically one-syllable seed sounds that, when said aloud, activate the energy of the chakras in order to purify and balance the mind and body. When you chant the bija mantras, you resonate with the energy of the associated deity.
The bija mantra "Dum" is associated with the fierce form of Mother Divine, Goddess Durga, who is known for her protective powers. This mantra invokes her power and protection. It is believed to have a powerful impact on one’s inner strength and energy and is known to combat negative thoughts and unproductive mental chatter. By chanting "Dum," devotees believe they are invoking the energy of Durga to protect them from harm and to help them overcome obstacles.
The bija mantra "Dum" is often incorporated into longer mantras dedicated to Goddess Durga, such as "Om Dum Durgayei Namaha." This longer mantra is often used for invoking Durga's protection and to seek her blessings.
When you chant the bija mantra for Durga, it is important to do so with sincere devotion and an open heart. The power of the mantra lies in its vibration and the intention behind the chanting. It is often said that repeating the mantra with faith and devotion produces greater benefits than mere repetition without faith.
As with any spiritual practice, it is helpful to learn from a knowledgeable teacher or practitioner, especially if you are new to the practice of mantra chanting. It's also important to approach the practice with respect and an understanding of the tradition it comes from.