I was fiddling out with new Lightning experience. I created a Lightning page using the App builder and activated it. Its showing me in the mobile app but on lightning experience on desktop I am unable to view them. Is there something am missing?
It is currently not possible to create new standalone pages for the Lightning Experience using the Lightning App Builder. There is a self service pilot available to Developer Edition orgs to customize the record detail pages using the App Builder, see http://docs.releasenotes.salesforce.com/en-us/winter16/release-notes/rn_forcecom_lex_edit_record_home_with_lab.htm
The other option is to expose the Lightning Component directly (without using the App Builder) in the App Launcher by following the steps outlined by Mohith Shrivastava.
You will have to implement the interface "force:appHostable" for your component to appear in the lightning new experience
Follow these steps to include your components in Lightning Experience and make them available to users in your organization.
Create a custom tab for this component.
From Setup, enter Tabs in the Quick Find box, then select Tabs. Click New in the Lightning Component Tabs related list.
Select the Lightning component that you want to make available to users.
Enter a label to display on the tab.
Select the tab style and click Next.
When prompted to add the tab to profiles, accept the default and click Save.
Assign your Lightning components to a custom app.
Create a custom app and name it Lightning.
Select the Lightning app you created and then click Edit.
In the Custom App Edit page, select the components you want to include, click Add, and then Save.
Check your output by navigating to the App Launcher in Lightning Experience. Your custom app should appear in theApp Launcher. Click the custom app to see the components you added.
As of winter 16 there is no ability for adding to left navigation but safe harbor this will come soon in next release(BIG SAFE HARBOUR)