Our brain is constantly manufacturing thoughts from its previous experiences and the current situation.  The only time it’s not producing thoughts is when the mind is in “awareness” mode, like a life-threatening situation or encountering something of profound interest.  Through meditation and body awareness practices like yoga or martial arts the mind can be trained to focus on what you wish to focus upon, versus following a seemingly random thought.  Thoughts are like seeds and some manifest and flourish, and some wane and die.  What makes the biggest difference in determining which thoughts, or seeds, flourish and which die?  Consciousness, awareness, and power of attention and intention.  I for one am glad that everything I think does not manifest, as I have some very unholy and unproductive thoughts.  
Without meditation training, which thoughts, or seeds manifest and which die is largely random.  Key to this process is making our thoughts conscious and reducing our unconscious thoughts and actions.  Have you ever committed to something like losing weight, only to find your self in the refrigerator grabbing a sweet snack a few days later?  Or deciding this is the semester to get on the honor roll in school, only to find ourselves at a party on a school night a few days later?  We all have.  The mind runs constantly and without awareness it often leads to counterproductive activities that we are unaware of until it’s too late. Studies have shown that as much as 95% of our actions are unconscious, yet we are dumbfounded that we constantly sabotage ourselves.
Meditation is a practice of “watching” our thoughts, and growing our awareness.  It’s a practice that allows us to “take a pitch”, or let a thought pass through without impact or manifesting.  It’s a practice that allows us to be aware of our thoughts, and allows us to have a choice as to which thoughts are fertilized and fostered, and which thoughts simply pass though like bubbles in a glass of Champagne or a poor pitch.  It is also a practice that allows us to grow a “gap” between thoughts, and in these “gaps” simply be present which can help us grow awareness and experience joy.  You can think of meditation as gardening, in which we foster the thoughts we choose and discard the weeds, or thoughts we don’t choose to foster, develop, or follow.
Practices such as visualization, reading, or affirmation allow us to plant seeds we wish to develop and manifest. For instance, visualizing myself accomplishing a great deed like graduating from college causes the seed to be planted and fostered.  Reading a book entitled “How to Succeed at College” would plant seeds of successful actions. An affirmation like “I am an A student”, written perhaps 25 times daily reaffirms the thought or seed, and helps it grow.  The more someone can fill the mind with desirable and productive thoughts the less room there is for unproductive thoughts.  Performing these activities while simultaneously weeding out counterproductive thoughts through meditation is the most impactful. 
Interestingly, thoughts are energy, as everything is energy and thought energy can be manifested into something material or solid.  For instance, the thought “I want a new house”, supported with the visualization of being in the house; putting up a picture of your dream home where you can see it each day; reading a book entitled “Creating Wealth Through Home Ownership”; and complemented by writing an affirmation like “I enjoy being in my new home” 25 times each day, would be incredibly supportive of actually obtaining a new home.  Bringing awareness to your current finances and savings, credit rating, and other things that are part of the home purchase process, while simultaneously bringing awareness to the things which are counterproductive to purchasing a home, like an expensive vacation, not paying my bills on time (i.e. poor credit score) so they can be minimized are crucial to success.