Here's how the hypothalamus does this. It is a constant monitor of what's happening in the body. Taking in data related to hormone levels in the blood and neural circuitry it identifies and balances the physical environment by stimulating the release and development of hormones. Its most closely related structure in doing this is the pituitary gland.
As the hypothalamus picks up data, say the need for more thyroid hormone, it sends a hormone to the pituitary gland which instructs it to wake up the thyroid and make more thyroid hormone. When the hypothalamus gets information saying that the thyroid has indeed balanced itself back out, the hypothalamus tells everyone to chill out.
With our thoughts, we get a very similar scenario. Under fear, anger, or stress we send information to the hypothalamus that will then create a physical (in the sense of hormones) based on that condition. Those hormones then literally build the body based on that bit of data....fear, anger, or stress. Your thoughts have now become "things" in physical form.
Why is this important? Well, do you want a body built of fear, anger, or stress? Or would you rather build a physical form out of love, peace, and joy? I bet the choice is easy. And that's the best part of all, it's a choice!!!
What are you choosing to create?