Events are, effectively, messages generated by browsers indicating that a visitor to your page has done something. For example, when a visitor moves the pointer over a link, the browser generates an onMouseOver event for that link; the browser then checks whether it should call some JavaScript code (specified in the page being viewed) in response. Different events are defined for different page elements; for example, in most browsers onMouseOver and onClick are events associated with links, whereas onLoad is an event associated with images and with the body section of the document.
An action is pre-written JavaScript code for performing a task, such as opening a browser window, showing or hiding an AP element, playing a sound, or stopping an Adobe Shockwave movie. The actions provided with Dreamweaver provide maximum cross-browser compatibility.