Couples who use NFP to achieve pregnancy use signs in a woman's body to determine the fertile phase of the woman's cycle, which is the optimal time to conceive.
Couples can also use NFP to avoid pregnancy by determining the fertile phase and then choosing to abstain from intercourse and genital contact during this time. No drugs, devices, or surgical procedures are used to avoid pregnancy.
Since the methods of NFP respect the love-giving (unitive) and life-giving (procreative) nature of the conjugal act, they take advantage of God’s design for married love!

Video source: Natural Womanhood, a women's health literacy program.
Learn more at naturalwomanhood.org