You will hear back from your universities in the spring of the year you wish to enroll. There are three types of decisions:
Offer of admission
If you are accepted to a university, congratulations! The institution will likely send you information on how to accept their offer. Within the offer of admission will also be an outline of what financial aid or scholarship funding they will give you. You don’t have to accept or decline this offer right away. Unless you applied for an Early Decision, you will have until April 15 to consider your options. This is the National Reply Date in the US.
If you do decide to decline an offer, let the admissions office know politely and as soon as possible. You might end up applying there for a research position at a later date, so don’t do anything to tarnish the university’s opinion of you.
If you have to postpone your enrollment for a year, you can ask for a deferral. Make sure to ask the admissions offer for guidance as soon as possible. Not every university will be able to defer you, so there is a chance that you will have to reapply in the coming year.
Being waitlisted means you had strong enough credentials to be considered for admission, but there were more competitive applicants in that admissions round. There is still a chance you will be offered admission. If a student who was offered admission declines their place, the university will return to the waitlisted candidates. Make sure you follow instructions on how to remain on the wait list.
A rejection is definite. The best advise we can give you is not to take it personally. The admissions committee faces the difficult task of choosing a limited number of talented and motivated students from a very large pool. This is not easy.
If you have received an acceptance letter to more than one institution, you need to make your definite choice and inform all other universities as soon as possible. Once you have figured out your finances and are able to prove that you can afford the year, the university will send you the forms you need to apply for a visa at the American consulate.
Once everything is finished, you can start your studies in America in September.
Some schools offer the opportunity to start halfway through the year (mid-year admission). If you rely on scholarships to finance your studies, this might not be an option for you. Most scholarships are not given out to people who start their studies mid-year.