A friend and I were discussing meditation the other day and she asked what the purpose of mantras and mudras were. A mantra can be thought of the same as an affirmation, or a line of thought that you want to repeat until it sinks into your brain and your belief system. I use several mantras during my hour of meditation twice a day. I use them in a particular order because they have become my trigger to create the inner space for me to access heightened awareness. The same with the mudras, or hand gestures. When you put your hands together in prayer, that is called a mudra.
When I sit to meditate, I typically sit Indian style (half lotus) on a cushion, with hands on knees, palms up, thumb touching my index finger in what is known in the yoga tradition as the Guyan mudra. The mudra is also a trigger for me. A trigger to elicit states of calm and receptivity. A trigger to contemplate how I act and react in this world. A trigger to consider and implement any changes I feel I want to make. The mechanics of making these changes is via changing (programming) the neural pathways in my brain. Below is an excellent article on how mantras and mudras can help you do just that.