Transitioning from high school to a 2 year college or 4 year university is sometimes overwhelming for many students especially if nobody in their family has attended college previously. In the K-12 educational system, the school has the responsibility to identify, test, and provide services for students who have disabilities. This system operates under federal guidelines established under the IDEA. In the post-secondary education system, we are guided by the Rehabilitation Act of 1973 section 504 and the American's with Disabilities Act (ADA). These laws are extremely different from IDEA and they place the responsibility on the student to self identify if they have a disability, produce documentation of their disability, and to request services from the college or university to obtain classroom accommodations.
Below are a few websites that will provide you with information regarding the transition process and may answer many of your questions.
Association on Higher Education and Disability (AHEAD)
Office of Civil Rights, U.S. Dept. of Education
Life After IEPs