It depends on where you live. Owning a car in a city, i.e. New York, Chicago, San Francisco, Seattle is less common than owning a car in a more rural community. Where I live Raleigh/Durham North Carolina, almost every family owns at least 1 car. I would say the majority of households own two cars. In the US you begin driving when you are 16 and it is not uncommon for a 16 year old to get their own car too. This is all dependent on where you fall on the household income spectrum. If you have less money you are less likely (for obvious reasons) to own a car. The strange thing is that it often costs more to insure a car than it does to purchase one.

We have public school bussing systems for kids in most places for primary - high school. Most cities have some sort of bussing system.

To your question "Do all Americans own cars" -outside of large cities where it's impractical, yeah...pretty much.

From wikipedia

In 2001, 70% of Americans drove to work in cars.[4] New York City is the only locality in the country where more than half of all households do not own a car (the figure is even higher in Manhattan, over 75%; nationally, the rate is 8%).