Keyboard help:
Press S or P to start/pause the slideshow in a photo gallery.
Press Z or L , or click inside the image in a photo gallery to "zoom" it (it "turns the lights off" allows looking at the images with less distractions, and the picture can be viewed at full resolution).
Press T to scroll the page to the top (also stops the photo gallery slideshow and shows the main menu).
Press left arrow key to move to the previous photo in a gallery. Works in "zoom" mode too.
Press right arrow key to move to the next photo in a gallery. Works in "zoom" mode too.
Press ESC or X or click the 'x' on the top right corner, or the black surroundings of the image to exit the "zoom" mode.

Photo gallery bottom "filmstrip" help:
Leave the mouse over one of the small images to show the title of the picture. Click on the little images in the strip at the bottom of the screen when in a photo gallery to immediately show the corresponding photo and its description.
When you move the mouse at the extreme left or right of the filmstrip an arrow may appear: click them to change page in the gallery. Works when the width of the browser window is not enough to contain all the thumbnails.
Below the gallery, comments are hidden while the slideshow is playing or the gallery is "zoomed". Stop the slideshow and exit "zoom" mode to show comment section again and use it.