How to Activate WordPress Plugins
All plugins listed on the WordPress Plugins page are either active or inactive (except the Drop-In plugins, which are active by default). Before you hope to use a plugin, you must activate it. When you want to activate an inactive plugin, follow these easy steps (in this case, you are activating the Subscribe to Comments plugin):
Click the Installed Plugins link on the Plugins menu.
The Plugins page opens, listing all the plugins you have installed in your WordPress blog.
Locate the Subscribe to Comments plugin.
If you have a lot of plugins installed on your WordPress website, you may have difficulty finding a recently installed plugin that you want to activate. You can narrow your search by clicking the Inactive link, which lists the currently inactive plugins.
Click the Activate link below the plugin name.
The Plugins page refreshes, and the Subscribe to Comments plugin now appears as an active plugin on the page.
If you’ve followed all these steps in your own WordPress blog, congratulations — you now have Subscribe to Comments installed. Great job! Now, go check out what your newly activated plugin can do for you and your blog.