Perhaps ask specific questions,
High schools vary greatly across the USA. The over whelming majority of kids go to public school. Many private schools are religious
Public schools can be very large or quite small. Some have more facilities than others. Our HS has a student population of 2120. The largest HS in our district has 3000 students. Our HS has a two gyms, a weight room, two indoor tracks, one out door track, football field, 3 baseball fiends, 6 tennis courts, a theater, band room, orchestra room, choir room, cafe, tutoring center, library, auto shop and sewing /cooking lab classes.
Students start classes before 8am. Many student do some kind of activity, club, organization, sport.
Our school is on the block system, four classes each semester. One semester of algebra 1 counts as one year. Classes are almost 90 minutes. Not many US schools are on the block system. Or their block system can work differently. My kids loved it. Most students have 7/8 classes per day, We had a closed campus. Student stayed in for lunch.
Atmosphere can be wildly different. From an inner city HS to a small HS out in farm country to a large HS in the burbs.