What classes do you need to take in college if you want to be a engineer ?

What classes you take depends somewhat on what type of engineer you want to be. For example, the classes for becoming a civil engineer will be different from the classes for becoming a computer engineering and both will be different from classes for becoming an aeronautical engineer.

However, that said, there are definitely similarities--in particular, you have to math--calculus, linear algebra at least.

If you want to get a more concrete sense of things, take a look at the degree requirements for these majors at MIT:

Chemical engineering

Electrical Engineering and Computer Science

Aerospace Engineering

Civil Engineering

Engineering students start out taking mostly the same courses in math and science, so that is not a decision you have to make this early. The school will require certain courses in math, physics, chemistry, and introductory courses in engineering. By the second year or so, students start to take slightly different courses emphasizing engineering specialties like mechanical or electrical engineering. Many of the courses are required by the speciality. For example, all electrical engineering students will take courses in electronics. As you move through the curriculum, you will get a better idea of what speciality you like. A lot of the choices about specific courses are made for you as determined by the area of specialization that you declare. There are elective courses, meaning the decision is entirely up to you, but you will get a lot of advice from other students who have taken the courses, from counselors, and from the professors. And by time you begin taking super-specialized courses, you will have been in college for a couple of years and will have a much better idea about the specific type of engineering you want to practice on the job. Engineering is considered a "professional school", which in academia means it is geared towards preparing students for a specific career. All of the courses you take, whether chosen by you or required by the curriculum, will prepare you for your career. I still use everything I learned in school every day on the job.

Aisha,
As the others have said the classes in college will depend on the engineering concentration you choose. Right now in high school, you should be heavily focused on STEM classes and electives. AP Physics, AP Science, AP Calc BC.