Gradually more collections will be added. Not all images or Albums will be displayed as part of a collection.
When you open an Album there are three alternative methods of viewing the Album displayed at the top right:
As a Slideshow - icon is like a computer screen with a play button. You can pause/continue the Sldeshow using the space bar. Or click or touch the pause/play button at the centre of the image.
As thumbnails - icon is like a brick wall.
In a larger size - icon is like a coloured square.