To Customizing a Master Page in sharepoint 2010,follow the below steps.
Step-1. Open SharePoint Designer and open your SharePoint site.
Step-2. In the navigation pane, click Master Pages.
Step-3. Click Blank Master Page, and provide a name for your master page (for example,
Step-4. Open the Foundation Starter master page in Notepad. Copy and replace the code from the downloaded master page to your new master page while in code view.
Step-5. Toggle to design view to see the master page as it would look in the browser.
Step-6. To set this master page as the default master page for your SharePoint site, click Master Pages in
the navigation pane. Right-click the master page and select Set as Default Master Page.
Step-7. Browse to your SharePoint site to test the look and feel of your new master page.