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.
Tabs allow you to separate content into neatly tabbed sections. This allows users to access new content without loading entirely new pages, which saves on bandwidth, and speeds up browsing. You will need to be comfortable editing HTML code to implement this.
Image Overlays (Lightbox Effect)
Image overlays allow you to show a larger version of an image in an overlay on the current page instead of causing a new page to load.