On a computer?
You can use the up key on your keyboard to step forward, and click and drag with your mouse to change your view.
On a phone?
You can move your phone around to change your view, and press on the screen to step forward
You can use the arrow buttons at the bottom of the screen to jump between rooms in the gallery.
When you look around the gallery you'll see a Read More button at the bottom of the screen and you'll discover more about the Artwork you are looking at.