Easy Tooltip is a free wordpress plugin to add css tooltips to content on your posts and pages .It offers a tinyMCE shortcode GUI which will guide you through the entire process of a tooltip.
To install
Login to wordpress (wp-admin).
In your admin dashboard click plugins and select Add New.
Type Easy Tooltip in the search field and click Search Plugins button.
Install Easy Tooltip.
After the successfully Installation click the activate Plugin link to activate the plugin.
[OR]
Download Easy Tooltip wordpress plugin. Download link.
Unzip and upload it to your WordPress wp-content/plugins directory.
Login to wp-admin. In your admin dashboard click plugins and activate the Easy Tooltip wordpress plugin