What kind of bag do they use to school in america?

Are you asking about book bags or a purse? Really, either one is open to your choice & personal style. In our local high school, the students seem to use mostly messenger bags and backpacks. If you look at websites for Old Navy, GAP, Aeropostale, American Eagle, Abercrombie,etc you'll see what the latest trends are - just choose what YOU like best. Different parts of the country latch on to different fads - you won't find girls in South Carolina using the same sort of bag that a girl in California is using. Just choose what you like and what works best for you! Being an individual is far more important than getting the right bag.