It is simply getting in touch with your higher and inner self and feeling the purest vibration of what it is you are trying to do.
The intent behind a field can be something like create and stimulate stem cells in my body, create and stimulate stem cells in general, or it can have very specific programming as to how it does so, and the various physiological processes it activates in the body.
Sometimes more specific fields are more effective, although this is often not the case. Also, what might be an effective field for someone else to make for the general public might be different than what would be an effective field for you personally. For example, you could simply visualize yourself in perfect health at your ideal weight with lots of energy and whatever else you want, and holding this image in your mind, imagine that you are this way, and push this energy into whatever you are using as a receptacle.