When we hear or look at the phrase "Natural Family Planning" what comes to mind first? With the first word of the phrase being "natural," some people may, unfortunately, think that the only thing NFP has going for it is that it is not artificial. Sometimes this may even feed into the common misconception that the Church's main disagreement with contraception is that it is artificial. Other obstacles to understanding NFP come from mainstream culture's inherently contraceptive mindset.
To explain the above misconception, I think it is important to point out that "Natural" is not the main event of the phrase, "Natural Family Planning." In fact, "natural" is not an event at all-- it's a descriptor. Remember when learning grammar, being told to find the verb of the sentence to figure out what's going on with the subject? Well, in Natural Family Planning, both grammatically and ideologically, the subject here is a family and the action is planning. NFP is most importantly about planning a family. Planning is intended to mean anticipation of something actually happening eventually, not an act of indefinite postponement. Included in the planning are the important aspects of knowing how to do the planning and commitment to carrying out the plans. "Natural" is the adjective describing the means of carrying out the plans.
Being natural is important to the context of the family planning, but not in the way many may think. The "N" in NFP does not merely mean "not-artificial." This important descriptor not only signifies a lack of man-made intervention, but it conveys a context of God-established law. Natural law dictates that procreation results from sexuality. For this reason, the main purpose and intent of Natural Family Planning is to plan a family, and to do so in cooperation (not contradiction) with Natural Law. This is what it means to be "open to life." Being open to life does not mean that a woman ought to become pregnant as often as possible. It does mean that a couple ought not to take actions that directly interfere with the natural result of sexuality.
To most people, NFP (aided by the mistaken idea that it is meant solely to serve as Catholic contraception) is only a mindset that comes into play during the "let's not have a(nother) child yet" stage. However, the principle of abiding by natural law continues to apply once conception is being actively sought. The statement that procreation results from sexuality as a principle of natural law deserves more elaboration on this. As we know, artificial contraception is against natural law, not only because it is artificial, but because it intentionally severs sexuality from its natural (law) result. Just as sexuality ought not to be severed from its natural result, so too must sexuality's result not be severed from its natural source. Thus, the principles employed in Natural Family Planning, as an ideology based upon natural law, are applied to both ends of the family planning spectrum. When these concepts are ignored, there is a two-fold result. The result is a culture that is both contraceptive in seeing children as a burden to be avoided but also, paradoxically, one that has a view of human life so consumerized that children are also seen as things to be procured according to desire.
 For further explanation on being open to life, there is really good post explaining openness to life at Conversion Diary, by Jennifer Fulwiler