Colleges often allow you to accept your offer of admission online through the college's website. That is where you will also pay your enrollment deposit, if you have to pay one. The deposit holds your place in the school's upcoming class. You can also choose to accept your admission by mail, using a form provided by the college. Any method you choose has to be completed in a timely manner, as admission offers have a deadline.
Print out the admissions acceptance form from the college's website. Fill it out, and submit payment for your enrollment deposit, if you are required to pay one when you mail the admissions acceptance form to the college. Some colleges have other ways of accepting your admissions by mail. Purdue University, for example, requires only that you send in your deposit with a note stating your name and birth date.
Log into your student account on the college's website, using the information provided in your acceptance letter. You may have been assigned a username and password or a website to go to -- to set up your student account. Accept the offer of admission once you have set up your account and logged in. You can typically find instructions for navigating your school's particular admissions acceptance system on the school's website and in your offer packet.
Make your decision before the deadline. You may only have a couple of weeks from the date of your acceptance to make a decision. For example, California State University, Fullerton gives admitted students 14 days from the date printed on their admission letters to accept or decline their offers of admission.