Download Chainfire's "Sideload Launcher - Android TV". Install from the play store directly to your nexus player using the browser on your desktop or laptop. It will show up in the home screen and it will show all apps, including sideloaded ones.
Many apps do not support Android TV's leanback launcher but will work on it, including Now Browser. I believe the app needs to state it supports Android TV in the manifest in order for it to appear on the home screen.
You could load a different launcher as suggested by Dante087 or just launch it from the setting/apps area.