The new Samsung Galaxy S6 is a great little phone, but unlike others, you can't remove the battery. This is, of course, a problem if your phone freezes and you want to get it going again. With most phones, you remove and pop the battery back in, and you're away.
So what to do if you've got an unresponsive S6?
The simple answer is to do a soft reset. You do that by pressing down the power button for around 6 seconds and it should turn off.
If that doesn't work, don't worry. Press and hold the power key and the volume down key, simultaneously for more than 7 seconds, and that will restart your phone.
If you do that, your device should restart like nothing ever happened. All your photos and everything will be exactly where you left them.
If there's a bigger problem, your phone might reboot into the new maintenance mode. Here, you'll see options, which you can scroll through with your volume buttons. Here, you can choose 'normal boot', which will restart your phone as normal. Or, if want to get rid of a troublesome app, you can start it in 'safe mode'. Or, you can go for 'factory reset', which will delete everything off your phone and revert your handset to the state it was when you bought it.
Should all these things not work, and you don't want to get under the hood, then it is time to ring up the people you bought it from to see what they can do for you.