How do I activate screensaver using Apple TV 4th generation?

Pressing the menu button quickly three times will activate the screensaver.

Go into settings - general - screensaver.

Apple have changed this to just one press of the menu button from home screen now

I guess that was the very basic answer assuming that someone hadn't read the manual or gone through the manual. I set up a folder through iPhoto's that I want to use as screensaver... I go through the menu on AppleTV, I choose My Photos and the correct folder, but it doesn't appear to use or save that folder . Any ideas why ?

Make sure you've shared the photos through itunes (file - home sharing - choose photos to share). Computer needs to remain on and running iTunes when you select on Apple TV, it will take some time to cache

Thanks, just what I was looking for. Cheers