How are manual extensions different from automatic extensions?
Manual extensions require you to fill out additional information. Automatic extensions do not.
There is only one type of manual extension but many types of automatic extensions
Manual extensions cost more than automatic extensions
Automatic extensions require setup. Manual extensions do not.
Many extension types require a bit of set-up—those are manual. Some extensions are added automatically when AdWords predicts they’ll improve your performance—those are automated. No setup is required for automated extensions, so they don’t show up among your options when you’re creating manual extensions.
Extensions are a great way to expand your ad with additional information. They give people more reasons to choose your business. Extension formats include call buttons, location information, links to specific parts of your website, additional text, and more. Some of them can be created automatically, others should be added manually.
With automated extensions, AdWords automatically creates and shows it below your ad. Extensions tend to boost ad performance, making your ads more likely to be clicked.
However, many extension types require a bit of set-up—those are manual extensions. Extensions you choose should depend on your advertising goal. For example, if you want to get people to download your app, consider using an app extension
Read more here: https://support.google.com/adwords/answer/2375499