Starring a repository allows you to keep track of projects that you find interesting, even if you aren't associated with the project.
You can star or unstar a repository from the navigation bar with the star button:
Activity from starred repositories don't show up in your dashboard feed, so you don't have to worry about missing important notifications for things you are working on.
You can see all the repositories that you have starred by going to your personal stars page.
As with most pages on GitHub, the Stars page responds to a few keyboard shortcuts. You can move up and down the list quickly, or open starred repositories directly from the page.
To get a list of keyboard shortcuts, type
? anywhere on the page.