This tutorial will walk you through the activation and configuration of Jetpack. We recommend using Jetpack if you want to do some custom CSS for your site or if you want to easily create tiled image galleries.
If you aren't already in the Plugins section of your dashboard, navigate there now. Find Jetpack in the listing, and under the name, choose "Activate."
You should be taken to a screen asking you to connect Jetpack to WordPress.com that looks like this:
Go ahead and click the "Connect to WordPress.com" button.