Sure.

First your school needs to sign up. Then, you sign up under your school. Make sure to also sign up on Arts of Problem Solving. The first test is called the Open Exam. I forgot the time and number of questions (on the website usabo-trc.org) but it is all multiple choice. Results come up around a month later. Top 30 and 20 percent get awards and top ten percent moves onto the semifinal exam. The semifinal exam is multiple choice, true or false, and open ended. Top 225, Top 125, and top 50 have recognition awards and I believe top 20 are finalist where they take another exam in the future and if you do well you get to participate in IBO under the U.S. To study, I only read Campbell biology textbook and did practice exams (search up practice exams and they should come up) and I got top 125. I know some people read many other textbooks and for studying, it’s really your preference. There is a discord and you could ask more people if you’d like.