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

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

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

Go into settings - general - screensaver.

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