Type your address and skip a space. Type the date and skip another space. Type the graduate coordinator's name, her title, the department's name, the university's name, and the department's address on separate lines. Skip an additional line.
Create the salutation by typing "Dear Dr. (graduate coordinator's last name)" followed by a colon. Skip another space.
Begin the letter by thanking the graduate coordinator for admitting you to the program, and name the program specifically. State that you accept the offer to start the program on the date or during the semester specified in the admissions letter.
Reiterate the details of the offer. For example, if you were offered a graduate teaching assistantship or a fellowship as part of the admissions program, state those details.
Close by thanking the graduate coordinator again, and tell her that you look forward to seeing her on campus. Give her your telephone number in case she needs to get in touch with you before then.
Type "Sincerely," and skip three lines. Type your full name. Print the letter and sign your name above your printed name.
Proofread your letter carefully. You do not want to make a bad first impression by having a letter with errors in it.
Check the date by which the admissions committee requested a response, and mail your letter with enough time to spare for it to arrive before that date. Many students also elect to pay for signature confirmation so they have proof of receipt.