Prismic documents are individual entities in your repository that can have multiple uses. A document can be an entire page on a website, a navbar, a banner, etc. This is defined in the Content modeling of your Custom types (the models that create the documents).
Publishing documents updates the API of your repository, and you'll be able to see the new data on your website.
Can you show me the website you're working on and which technology you are using?
Which Custom Types does your website use to create each page? You probably use a particular type to publish each one.
If your site is configured to automatically detect new documents, you could publish a document in your repository and the site should rebuild the project to reflect the changes.
Yes, in the documentation you didn't mention that the type "page" is created by the author. ( example - video). So I just created the type "custom-page" via "Custom Types". Prismic docs and vids should be remade.