Every page in the CMS has a set of fields that allow you to define custom SEO metadata for that page.
The <title> is controlled by the Title field at the top of the field list:
Under the Page Meta Properties section, you can find two fields for controlling the page description and keywords. Multiple keywords should be separated by commas.
There are also specific field sections for controlling OpenGraph metadata, which is used when sharing pages on Facebook and other social media sites that use the OpenGraph standard. There is also a specific set of fields for Twitter metadata. This overrides the OpenGraph tags when sharing pages on Twitter.
Finally, for all other types of metadata, there is the Custom Metadata section. This allows you to enter an arbitrary list of name-value pairs that will be inserted into the page <head> as <meta> tags. This can be used for a variety of purposes. One specific example would be telling Google not to index a particular page, which can be done using robots as the meta name and noindex, nofollow as the meta value:
Note: Sitecore automatically inserts the correct canonical URL (<link rel="canonical">), so you don’t have to manually add this.