Upload the stackoverflow-flair-widget directory into your /wp-content/plugins/ directory.
Activate the plugin through the 'Plugins' menu in WordPress.
Add the widget to your sidebar through the 'Widgets' panel under 'Appearance'.
Configure the widget. At minimum, you should specify your User ID. If you're not sure what your
user ID is, login to Stack Overflow and view your profile. Your user ID is the number in the URL.