Content rules are an advanced function of the web system that allow you to set automatic actions to occur whenever a user does something specific. For instance, you can set up email alerts to be sent every time an item is published on your site.
The version history of items such as pages, images, news, etc provides a list of all the edits/changes made to such items. Each time changes are made to an item, a new version is saved. These various versions will then be listed under "History".
jQuery Tools is a collection of user interface plugins that allow you to achieve effects like tabbed content, lightbox-style overlays, and tooltips. These effects are already built into the web system, but they're implemented through the editing of page HTML.