Visualizing is the process of bringing to your mind the thoughts and emotions associated with the desired reality you prefer.
The more you can see, in your mind's eye, the way you want your reality to look the more you will draw to you what you desire. Our imagination is a powerful tool.
It's kind of like a placebo. In the sense that it does not matter if it is actually taking place or not, you see it taking place when you watch your video, ever increasing your belief, and eventually this manifests into your reality.
It has been scientifically proven that your mind does not know the difference between something that is actually taking place and something that is taking place only in your mind. It is why you are frightened when you watch a scary movie. Your mind believes it to be actually taking place.
Seeing yourself in your mind's eye being and having what you desire is tricking your mind into believing it is actually taking place. It raises your belief and sparks further thought and emotion then the Universe matches like energies until the manifestation of what you desire becomes your reality.