Two agencies within the U.S. Department of Labor enforce parts of the ADA. The Office of Federal Contract Compliance Programs (OFCCP) has coordinating authority under the employment-related provisions of the ADA. The Civil Rights Center (CRC) is responsible for enforcing Title II of the ADA as it applies to the labor- and workforce-related practices of state and local governments and other public entities. Visit the Laws & Regulations subtopic for specific information on these provisions.

The ADA has four main components: (1) requirements for maintaining medical records and requiring medical testing, (2) an employer must reasonably accommodate disabilities, (3) an employer may not discriminate against an individual with a disability, and (4) an employer may not retaliate against someone who opposes discrimination of participates in protected activity.
Under Title III, no individual may be discriminated against on the basis of disability with regards to the full and equal enjoyment of the goods, services, facilities, or accommodations of any place of public accommodation by any person who owns, leases, or operates a place of public accommodation. Public accommodations include most places of lodging (such as inns and hotels), recreation, transportation, education, and dining, along with stores, care providers, and places of public displays.
Title IV of the ADA amended the landmark Communications Act of 1934 primarily by adding section 47 U.S.C. § 225. This section requires that all telecommunications companies in the U.S. take steps to ensure functionally equivalent services for consumers with disabilities, notably those who are deaf or hard of hearing and those with speech impairments. When Title IV took effect in the early 1990s, it led to the installation of public teletypewriter (TTY) machines and other TDD (telecommunications devices for the deaf). Title IV also led to the creation, in all 50 states and the District of Columbia, of what was then called dual-party relay services and now are known as Telecommunications Relay Services (TRS), such as STS relay. Today, many TRS-mediated calls are made over the Internet by consumers who use broadband connections. Some are Video Relay Service (VRS) calls, while others are text calls. In either variation, communication assistants translate between the signed or typed words of a consumer and the spoken words of others. In 2006, according to the Federal Communications Commission (FCC), VRS calls averaged two million minutes a month.
Hey OB – Disclaimer – none of this is legal advice and you’d want to check with a lawyer to know if you’re at risk for any action if you’re not ADA compliant. Based on what we’ve seen if you don’t have a physical retail or service location, and you don’t receive any funding from the government you likely aren’t required to have a website that would be considered compliant. Some people expect that to change in the next few years, but that’s what we know for now. Let us know if you have more questions or would like to test your site.

I should mention one caveat to all of this. Businesses that are required to comply but don't have the ability to bring their websites into compliance can provide an accessible alternative to provide the same information, goods, and services that they provide online, like a staffed phone line. The trick, however, is that this option has to provide at least equal access, including in terms of hours of operation. And, as we know, the internet is around 24/7, so good luck with that. 
As a result, most ADA suits are brought by a small number of private plaintiffs who view themselves as champions of the disabled. For the ADA to yield its promise of equal access for the disabled, it may indeed be necessary and desirable for committed individuals to bring serial litigation advancing the time when public accommodations will be compliant with the ADA."[57]
Videos need to incorporate features that make them accessible to everyone. Provide audio descriptions of images (including changes in setting, gestures, and other details) to make videos accessible to people who are blind or have low vision. Provide text captions synchronized with the video images to make videos and audio tracks accessible to people who are deaf or hard of hearing.
While legal considerations might be your biggest worry, making your site more accessible is simply good customer service. More than 39 million Americans are blind and another 246 million have "low vision," Another one million are deaf in the U.S. Add to that people with mobility issues that prevent them from using their hands and that's a huge portion of the country's buying power.