Your question is very brief, it sounds like you're trying to create a new page layout? If that's correct you need to also declare it in layouts.xml
.
Official documentation
How to Create a Custom Page Layout
Add your layout
In this example I'll create a layout named Test Layout, it's the exact same as the one column layout but you can add your own here.
Create this file (changing the name to suit your layout):
app/design/frontend/**VENDOR**/**THEME**/Magento_Theme/page_layout/test-layout.xml
Content:
<?xml version="1.0" ?>
<layout xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="urn:magento:framework:View/Layout/etc/page_layout.xsd">
<update handle="empty"/>
<referenceContainer name="page.wrapper">
<container name="header.container" as="header_container" label="Page Header Container" htmlTag="header" htmlClass="page-header" before="main.content"/>
<container name="page.top" as="page_top" label="After Page Header" after="header.container"/>
<container name="footer-container" as="footer" before="before.body.end" label="Page Footer Container" htmlTag="footer" htmlClass="page-footer" />
</referenceContainer>
</layout>
My test layout is based off the empty page layout so it's starting from scratch, you can also create a layout based another layout, such as 2columns-left or 3columns. To do that just replace <update handle="empty"/>
with the layout you wish to use, e.g <update handle="3columns"/>
Inform Magento of your layout
Create this XML file:
app/design/frontend/**VENDOR**/**THEME**/Magento_Theme/layouts.xml
This is where you declare your custom layouts, like so.
<page_layouts xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="urn:magento:framework:View/PageLayout/etc/layouts.xsd">
<layout id="test-layout">
<label translate="true">Test Layout</label>
</layout>
</page_layouts>
And now we can use our new layout either in the XML or the admin: