Admin Flush W3TC Cache works with the W3 Total Cache plugin. It simply adds an "Empty All Caches" option to every Admin page.
It's not a button, it's a text link. Assuming the plugin is enabled and working properly, the link should appear at the top right of your screen (for LTR languages, left side for RTL languages).
Click the link from any admin page and all caches will be cleared.
You will be returned to the same page you were on when you clicked the link, and you should see the standard W3TC notification that the caches have been cleared.
There are no settings, just enable the plugin and the link appears.
Admin Flush W3TC Cache requires that the W3 Total Cache plugin be installed and active. If either of these conditions is not true, the link will not appear. Please ensure that you have installed the W3 Total Cache plugin and that it has been activated.
Update to Admin Flush W3TC Cache version 1.2 or greater. Version 1.2 fixes compatibility with W3TC 0.9.2.4 and above.