The Reader is designed to be simple to use.
You can swipe between pages using your fingers - just swipe left and right.
Use a pinch gesture to step through 3 different preset zoom levels; a small, default and large view. Note that this will re-flow the layout of the music. The Reader will also remember your zoom preference between scores, so you can set-and-forget.
You can also use a bluetooth page turner device to turn the pages left and right, or use the arrow keys or page up/down on your keyboard, to flip between pages.
If you have imported a score locally, you can set the playback position by double-tapping a bar with your finger. You'll see the bar-line highlight in blue to indicate it'll playback from that position. You cannot do this in ScoreSync, since StaffPad is in control of the playback position.