It defines the sort of tools, talents and abilities you have available during this incarnation. From your full name at birth through to your date of birth, one can determine your Divine purpose for this lifetime and identify your character strengths, weaknesses and most favorable career areas. You can also discover which Karmic Lessons you will face this lifetime and learn how to face and handle their testing circumstances. Overcome these past life shortcomings and you will move your soul's final graduation day light years ahead. They themselves don't make anything happen.
Numbers simply indicate.
There is a hidden pattern or rhythm to the whole of life. Numbers and alphabets reveal this pattern to us. Every number and letter has its own vibration and meaning. Numerology is using time honored fomulas and calculations to find out how these vibrations affect our lives and time our decisions to them.