Who this is for. A theme developer who has deployed a placeholder template and now needs a layout to point at it. After this page you will have a page layout called Article, and know what each field of the layout form decides.

The form

Open Customization › Layouts and add a layout. The form's fields:

FieldFor the articleWhat it decides
NameArticleThe name editors see when they choose a layout, and the one you find it by in the admin
Identifierarticle, or emptyOptional. A stable name for reading the layout through the API; it must be unique
SiteEmpty, or the siteShown only when the client has more than one site. Empty makes the layout available on all of them
ControllerShow Page, under PagesWhich kind of record may use the layout; see below
Templatepages/pages/article.htmlThe file the layout renders with, chosen from a tree of the files the admin finds in the site's templates/ folder on the server
AreasOn the next pageThe fields editors fill in

If pages/pages/article.html is not in the template tree, the file has not reached the server: go back to Commit and deploy it. The tree is read from the server each time the form opens, and offers only the files it finds there.

The controller makes it a page layout

The controller is what turns a layout into a page layout: when an editor creates a page, the layout list offers only layouts whose controller is Show Page under Pages, and leaves out hidden ones. Left at None (Component), the layout becomes a component layout, for blocks placed inside other records, and never appears when a page is created. For a template under components/, the form does not offer a controller at all.

The other choices, for the other kinds of record a layout can render:

GroupControllers
BlogsList Blog Posts, Show Blog Post
BooksShow Book, Show Unit, Show Book Page
FAQShow Page, Show Question
FormsShow Form
PagesShow Page
ProductsList Products, Show Product, Show Product Category

There are two Show Page choices, one under FAQ and one under Pages. For an ordinary page, pick the one under Pages.

Save, and check

Save the layout. Then open Content › Pages and start adding a page: Article should be in its layout list. If it is not, the controller is wrong or the layout is hidden. Keep the page form for Create and publish a page; first give the layout its areas.