Like most Microsoft programs since Office 2007 was released, Windows Live Mail 2012 (the latest version) comes with a "ribbon" instead of the traditional toolbar. This also means that its "title bar", the strip at the top of the window that includes the minimize, maximize/restore, and close buttons, comes with enhanced functionality. This is called the "quick access toolbar", in Windows Live Mail as well as any other app that includes it. The screenshot shows the quick access toolbar once you press the Alt key on your keyboard: doing so shows all the keyboard shortcuts available. Notice that each command shown in the toolbar can be activated with a number!
By default, the quick access toolbar only includes three commands: compose a new message, reply to the currently selected email, and "update all" - which means check for new mail for all accounts, and any RSS feeds to which you may have subscribed: 
Tip: because common commands are available in that toolbar, you can regain screen real estate by hiding the ribbon from Windows Live Mail's main window!
To customize anything in the quick access toolbar, just click on the dropdown arrow button on the right, as shown on the screenshot. This will open a menu, with a complete list of commands you can show or hide in the toolbar. Checked items are visible, unchecked items are currently hidden. Just check or check as needed to add or remove command buttons from the toolbar! 
These keyboard shortcuts are very easy to memorize: activate the first command on the left by holding down the Alt key and hitting the number 1 on the left side of your keyboard (not the one on the numpad, in other words!) The second command from the left automatically gets the Alt+2 keyboard shortcut, and so on. These keyboard shortcuts are updated whenever you hide or show new commands in the toolbar. Refer to this screenshot for the note below.
Note: if you can't remember a keyboard shortcut, whether in that toolbar, or in the ribbon, just hit the Alt key alone. This shows you the next key to hit!
Like many new Windows programs, you can move the toolbar below the ribbon. To do so, click on the dropdown arrow button: this time, select the "Show below the Ribbon" command option at the bottom. With the ribbon minimized, here's what it all looks like. Notice that some vertical space is wasted, since the quick access toolbar is no longer combined with the title bar: 
Final Tip: along with hiding the ribbon, you can also get more space on the screen for your emails by hiding the calendar pane. (Unless you're always working with dates, you can always view your calendar by hitting Ctrl+2!)