Mantra is a sound formula. It is a vibratory composition. Commonly people understand stutis and shlokas as mantras, but real mantras do not carry any dictionary words.
A mantra is just a sound graph.
There are three types of mantras: female, male and eunuch. Each type of mantra creates its own effect.
What will you realize by mantra? First, it will take you out of the tormentation you suffer due your thoughts and you will have a new vision. The new vision will be that the cosmos is not anything but Shiv and Shakti; sat and chit; station and motion.