Sometimes your WordPress site feels slow. This plugin helps you diagnose issues by measuring exactly how long the PHP script takes to generate a page. Simply install and activate; then, view the page source to find the execution time at the very bottom. No configuration needed.
Extract the zip file and just drop the contents in the wp-content/plugins/ directory of your WordPress installation and then activate the Plugin from Plugins page.
For more details,
http://codex.wordpress.org/Managing_Plugins