According to Indian vedic literature mantra are a group of words, sounds that is capable of creating a transformation in yourself. This transformation varies according to the type of mantra used
Mantra is oftenly used in meditation to awaken various chakras of the body.
for example: The third eye chakra . the mantra " om" specifically used to awaken this chakra.
Repeated use of the mantra while concentrating on it leads to the awakening of the chakra.
There are several chakras . Once you awaken all of them you awaken your inner self