Gallery Navigation.

Clicking ONCE on an image will bring up a larger image.  Pressing the play (►) icon at the top left of the larger image will start a slideshow of individual images.  The slideshow can be paused at any time by clicking the pause ( II ) icon.
Pressing the ESC key or clicking ONCE anywhere outside the displayed image will return you to the thumbnail view.

Clicking the close ( x ) icon at the top right will close the image.
Clicking on an image, using the keyboard left/right arrows or the arrows on either side of the screen will reveal the next image.
Moving your mouse until you see the hand icon then left clicking will also advance the image.
The slide show can be paused or resumed at any time.