Principle has a template for the Categories (tags) page, which shows all of the categories (tags) of your publication. A categories page is not required, but you can add it if you want.
To create the Categories page:
Go to Pages from the admin menu
Click the New page buttonin the top right corner
Add Page title (e.g. 'Categories' or 'Tags')
If you want, you can add featured image for this page
Click icon in the top right corner to open the Page settings
Add a small description text (inside excerpt) if you want
Click the Template selector and choosethe Categories option
Click Publish
Starting with Ghost 6.0, themes will only receive a maximum of 100 categories for display on categories page.