From Setup, click Creating a custom tab is a prerequisite to enabling your component in the Salesforce1 navigation menu, but accessing your Lightning component from the full Salesforce site is not supported. An administrator has to add the custom tab to the navigation menu in Salesforce1 by clicking from Setup. For more information, see “Adding Lightning Components to Salesforce1” in the Salesforce Help. to create a Lightning Component tab.
For more information on Lightning components, see Lightning Components (Beta).