Add Google Analytics code to your blog / website in less than 5 minutes using this easy to follow video tutorial. Besides being able to get an insight into the demographics of your visitors, web analytics also help you monetize your blog / website by showing off your analytics charts and data to potential advertisers.
As far as adding the analytics code goes, I recommend the manual way (#8 below) and not the plugin way (#7 below). Why? Because each plugin you install on your blog could potentially slow down your blog’s performance, so you should try to accomplish everything you want on your blog without a plugin (for example, by looking for widgets and HTML or PHP code that will accomplish the task in hand) and turn to plugins only if all else fails.