HPV is generally acquired in adolescence (age 13 and up) or early adulthood and is passed from person to person through physical contact. In most cases, infection is asymptomatic (causes no discomfort) and spontaneously cleared in weeks to months. For unknown reasons, it persists in some persons, and infected sites become cancerous 20-40 years later when people are in the prime of life.
The incidence of oral infections and cancers has declined significantly as well. In addition, HPV causes genital warts (condylomata acuminata), and vaccination prevents these.
Vaccination against HPV is not mandated in the US, but that does not mean that it is not very important. The most significant barrier to vaccination is the failure of health care providers to recommend it and the failure of parents to request it. Essentially, it's up to you to ask for it!