How do I automatically add all the pages of a website to the database?

If I create a search engine and put in, for example, the Wikipedia url, only that home page will appear. How can I make it so that all the pages of a website are added to the database or that all the pages of a website appear in the search engine without having to add each one manually?
Is there any way of doing this? Because having to add each page of a website manually is impossible, even worse if it’s several websites.
I think Google uses a tracking mechanism to do this, I don’t know.