Access the Master Page Gallery in SharePoint 2010
A page layout is like any other kind of document in SharePoint 2010. It’s stored in a document library, has properties, and can be checked out, version controlled, and subject to content approval.
The document library where page layouts (and master pages) are stored is called the Master Page Gallery. You can access this library using either SharePoint Designer 2010 or the browser. To access this library from the browser:
Browse to your site collection.
Choose Site Actions→Site Settings.
The Site Settings page appears.
Click the Master Pages and Page Layouts link.
The Master Page Gallery opens.
Before you can start using your page layout to create new publishing pages, you need to check it in and approve the file.
Your new page layout is available to you and your editors when you create a new publishing page or change the page settings for a publishing page of the same content type.
When you or your users initially select a page layout and then decide to change the page layout later, you can make changes only to other pages of the same content type.
Therefore, if you have no specific need for a custom content type, choose the Welcome Page type so that your users can change the default home page of a site to your new page layout because the home page is usually some sort of welcome.