Smartglass is an app for Android, iOS and WP devices. download it from your app store, login with your Live ID (your Xbox one), and then it will connect to your home Xbox 360 and Xbox One (different SG app for each one). You can then control your Xbox - push files to it, look on the internet using your tablet or phone and push it to your TV.
Games also have some smartglass support - for example in BF4 for the XO you can get a top down view of the battlefield as a commander using your tablet - and use touch to issue commands.
Anyhow even with your smelly PS4 you can still log into the Smartglass app using your Xbox creds and even without an XO - still log in and see what all your friends are up to - and view their game clips etc.