Some colleges will directly admit you to a major. Some colleges might accept you to the pre-major, so you have to complete prereqs and then you are officially in the major.
Most colleges will ask for your major so you should put what you think you want to study, or put undeclared, but be aware: it might be harder for admission at some colleges.
Most colleges will assign majors so you need to select on the apps, especially colleges that choose you by major.