WordPress tooltip plugins lets you add tooltips to plain text and links on your post and pages.
It offers a tinyMCE shortcode GUI which will guide you through the entire process of a tooltip.
This plugin uses jQuery tipTip authored by Drew Wilson http://code.drewwilson.com/entry/tiptip-jquery-plugin.
You can also add tooltips manually by following the pattern below:
[tooltip content="This will show in a tooltip" url="This will make tooltip a link"]Hover over me for tooltip[/tooltip]
Url is optional. If URL is added, it will render a link otherwise it will be a plain text.
Download the plugin. Navigate to “Plugins -> Add New” and click on Upload link.
Use the uploader to upload the plugin zip file and click on “Install Now” button.
After plugin is uploaded. Click on “Activate Now” link to fully install the plugin.