Google tags set and read cookies to identify unique users across browsing sessions. Cookies are small files saved on peoples' computers to help store preferences and other information that's used on web pages that they visit.
Google uses cookies in various ways. Remarketing and Google Analytics both use cookies to help do things like run your ads or measure your success. The conversion measurement features of Google Ads and Campaign Manager also use cookies. To help you measure sales and other conversions from your ad, a cookie is added to a person's computer when the person clicks an ad.
For a detailed list of cookies used by Google, refer to the advertising and measurement cookie reference.
In most cases, the default cookie preferences don't have to be modified — Only make changes to these settings if your website requires it.