Fullscreen at the top of the window fills the screen with the image, this then becomes Exit Fullscreen to reverse the action.
You can also press "Esc" to exit Fullscreen mode.
 

Click View Mode at bottom left to choose between .....

1. Scroll - view the magazine as a long scroll "up and down" the screen by ....

   1. dragging the right-hand slider up and down the screen

   2. clicking above or below the slider

   3. clicking on the small arrowheads above and below the slider

   4. using the á and â keys on the keyboard, or

   5. using the mouse wheel

2. Book - change pages in a turn-over action by clicking bottom left and right corners

3. Slide - change pages in a slide-change action by clicking bottom left and right corners
    

Zoom "-" and "+" changes on-screen magnification. 
 

Not sure what the left icon does. The right icon shows all the pages as small images, you can click on a page and go straight to it.

View the magazine as a long scroll "up and down" the screen by ....

1. dragging the right-hand slider up and down the screen

2. clicking above or below the slider

3. clicking on the small arrowheads above and below the slider

4. using the á and â keys on the keyboard, or .....

5. using the mouse wheel