The etymology of the word mantra is “Manan??t tr??yat?? iti mantrah” — which means repetition (Manan??t) of that which protects (tr??yat??).
Taking a quick step back — to understand mantras, we need to first know the origin of Sanskrit letters which constitutes it. The 57 Sanskrit letters are believed to come from 14 categories of sounds that came from Lord Shiva’s damaru (a musical instrument that Shiva holds in his upper right hand in the Nataraja form) and are referred to as Maheshwara sutra.
Coming back to mantras, each mantra is constituted of Shadanga (six elements)