Simply follow the following steps to realize how mantra works:
- Call some people around you and tell them to sit independently in a peaceful place.
- Prepare them to feel and do whatever you say.
- Tell them to close their eyes and imagine their own body in mind.
- Tell them to imagine that they are playing with sand and pebbles with their long nails in a bank of river.
- Tell them to imagine that now they are robbing their hands with nails with bits of sand on a iron gate.
- After repeating the lat stage several times, tell them to open their eyes and ask them 'Did you find any movement inside your body?'

Obviously most of them experienced their body moving. This is the way the Mantra works. Your all instructions were Mantra spelled by you and the movement of the body of those guys was the effect of Mantra.

You may tell me that those sentences were general English words which do not seem to be any type of Mantra and then you may give me some Sanskrit words {mantras} to illustrate how actually mantras are. But have you ever translated those Sanskrit mantras into any other language you know well? They have similar value like you spell some English sentences above. Hope you understand what a  mantra is and how it works.

Disclaimer: This article does not support the existence of Mantra. It only advocates the power of word.
Discovered by +Don Prince