Most of the touchscreen functions are not discoverable. Pinch-to-zoom, long-press, swiping with multiple fingers, etc. It's very easy to do though, not what I would call a power-user thing. Remember there is only one physical button on the front of the device, and this is one of the things that it does.
At least for some features like pinch-to-zoom they included very clear examples in the massive ad campaigns. I don't remember seeing this feature in an ad but it wouldn't surprise me. At least it's on this page https://www.apple.com/iphone-6/design/
