Search Ads
These are text based ads that show up on the results page of the search engine queries. They are sometimes placed on other websites as well.
Display Ads
Display ads are in the form of images and videos that are displayed on Google's network of websites.

Shopping Ads
These are rich media ads that contain information about the products and are shown to people who have an intent to buy.
Remarketing
Remarketing ads target people who have already visited your website and have shown an interest in your offerings.