Google AdWords extensions are a very important part of their ad platform, and as an advertiser, you SHOULD be using as many of them as possible for your ads.
To make it easy for you to find what each extension is and how you should use it, I’ve taken the liberty of creating a blog post with Google’s AdWords team explaining what each one is and how to use it.
How to extend your Google Ad with a phone number:
How to add Site Links to your Google Ads:
What are Structured Snippets and how do you extend your Google Ads with them:
How to add Reviews to your Google AdWords Search ads:
How to add Seller (Star) Ratings to your Google ads:
How to use/add Callout Extensions to your Google Ads: