This website provides ADA Documents which cater to several different domains, such as Private Business, Facility Access, Recreation Access, etc. It also provides a general search engine which searches through the website to help you find what you're looking for. The Frequently Asked Questions provides very good insight on questions you may have regarding ADA guidelines, and who is required to follow them.
The federal government website for the ADA features information for all domains relating to the ADA, including accessibility. You'll find information regarding state and local government guidelines, as well as Frequently Asked Questions about ADA guidelines. This website also provides all information in Spanish (Preguntas y respuestas respecto a la Ley sobre Estadounidenses con Discapacidades).
Please refer to this website if you are interested in the technical requirements for Platform lifts. This will link you to the ADA Accessibility Guidelines for Buildings and Facilities (ADAAG), Section 4.11 - Platform Lifts (Wheelchair Lifts).