This plugin is the default plugin in your WordPress and just pending for activation. Activate the plugin and proceed to step 2.
Go to Akismet.com/signup/ and register for “Personal plan”.
Once registered, an API key will be sent to you via email.
Go to your WordPress control panel again and click on “Akismet Configuration” under “Plugins” tab. Enter the API key that you have just received and click “Update options”. If the activation is successful, it will shows “the key is valid”.