This a basic step for every site. There should be a topic in the forum on this. Please don't tell me to look at the documentation. The documentation is not searchable because "about" cannot be disambiguated by a search engine.
So if anyone would like to help every new WordPress user get this basic step done, please post here. Right now my template (the most popular WordPress template of all) creates a 404 error message when I click on "About" on the menu.