Imagine if you will for a moment a world where a blind person could walk up and talk a computer, vocalize and have a conversation, and never have to "see" a computer screen; or a person with no movement ability being able to send a mouse cursor dancing across their screen with the movement of their eyes, or better yet... just their thoughts. We're not there yet, but these things are coming; in the mean time, with the advent of social media and sites like Facebook and Youtube, the World Wide Web needs to be a more accessible place so everyone has equal opportunity to be a part of it, and with the right design practices a lot of people and companies are achieving a more accessible web presence.
So what are some of the steps taken to ensure an accessible web site for the public? Let's take a look at the basics to help with individual accessibility needs:
For a Person with Complete Vision Loss
Users with no sight at all must utilize a screen reader to read the content of your web page; the screen reader will go through a websites code (HTML) and decipher what needs to be read aloud and what to ignore. Making sure you have images marked with alt text and making sure your page tabs flows in a natural order will make it easier for users with screen readers, especially when navigating links with the tab key.
For a Person with Partial/Poor Sight
While most web browsers these days (See Firefox/Internet Explorer for instance) have built in magnification abilities (heck, if you're reading this on a computer right now, hold down your control key and and press the plus (+) or minus (-) keys to see exactly how your browser zooms), but they require some technical know how sometimes and may not work properly with all sites. To make a site more user friendly it's a common practice to put a text resizing tool on the site that allow users to pick their own font sizes and in some cases, change colors for high contrast/low contrast or for color blind users.
For a Person who is Hard of Hear
While most hard of hearing users can see the content of your site, media recordings (YouTube videos, audio recordings) are a different beast altogether; providing sub-titles or transcripts will make them accessible.
For a Person with Learning Disabilities
In order to be sure your content is available to all audiences, it's good practice to write content in a clear and simple format. Too much content on a page can prevent some users from being able to maintain focus.
While this only touches on the basic forms of accessibility, it's enough get a website to an accessible state at the start. Depending on where you are in the world, laws change regarding web accessibility and what must be done to maintain it. There are also many applications out there for the end user and more information for developers. If you wish to know more, I suggest a good jumping off point is the World Wide Web Consortium's (WC3) Web Accessibility Iniative found at http://www.w3.org/WAI/ .