Akismet plugin is a famous wordpress plugin which checks your comments against the Akismet web service to see if they look like spam or not. Now wordpress recommend to use this plugin and it is a default installed plugin when you install new version of WordPress.
You need an API key to use it. If you applied a WordPress API key before, you don’t need to apply a new API from Akismet. If you don’t have one API, and your blog is individual and not for business, you can apply a free Akismet API key from Akismet.
How to use ?
1. Download Akismet plugin if your blog doesn’t have , then and unzip. If your blog has already installed it. go to 3.
2. Upload the plugin file to your WordPress plugins directory inside of wp-content.
3. Activate it from the plugins menu inside of WordPress.
4. Your will see a message on the top to ask you Enter your API key.
5. Forget that spam was ever a problem.