How to Use in XAML
The easiest way to use the Segoe MDL2 (Microsoft Design Language 2.0) Assets font is with the TextBlock element.
<TextBlock Text="" FontFamily="Segoe MDL2 Assets" AutomationProperties.Name="Favorite" />
Some icons are broken into multiple icons and can be overlapped.
Creating Custom Glyphs
All glyphs in the font are produced on a 16x16 grid (a few toward the end are 32x16). These are all vector based so each pixel space could be comprised of more details when they are scaled. For example the keyboard has rounded edges.
Other Resources
Guidelines for Segoe MDL2 icons - MSDN
Segoe MDL2 Assets - XAML / CS Lists - Scott Lovegrove
Hamburger Menu Overview - Jerry Nixon