What a mantra is and how it works?

Could you please explain what a mantra is and how it operates? I'm curious about its origins and the ways it can potentially benefit individuals. Is it simply a repetitive phrase or does it involve deeper meanings and practices? Also, how does it work in terms of its psychological or spiritual effects? Could you elaborate on the scientific basis, if any, behind its purported benefits? I'm really interested in understanding this concept further. Thank you for your assistance.