As the name suggests, a responsive website responds to the environment in which it is being viewed. A responsive website is built for viewing on a computer (or non-mobile device), but is built with screen size in mind. It is a flexible framework that will adjust itself automatically to the size of the screen the user is viewing the site on, whether that be on an iPhone, an Android Tablet, a 13” laptop or a 27” screen.
The purpose of a responsive website is to have one site, on one domain, but having the elements of the site respond differently when viewed on devices of different sizes. For example, if you view a responsive website on a desktop, the content may be organised into three columns. When you adjust the screen size you are viewing the site on, these columns may collapse, or stack, to one column for a better user experience. Images will resize themselves automatically instead of distorting the layout or getting cut off.
Because a responsive site is just one site that behaves differently on different devices, the content will generally remain the same, regardless of how you are viewing the site (I say generally because there are ways to hide certain elements on mobile devices, for example large images that aren’t necessary to smaller screens and may slow down load times). But however you are viewing the site, you will have access to the same information and content, in full.