By default, you are in ‘Loupe View’ (E) which is where you see one main image and a filmstrip. You can toggle the position of the filmstrip between vertical and horizontal by pressing (Y).
To switch to ‘Grid View’, tap (G) or click the icon in the horizontal toolbar. In grid view the slider in the horizontal toolbar changes the size of the thumbnails.
To enter 'Scenes View' press (S) or click on the icon in the horizontal toolbar to view the images grouped into 'Scenes' (a set of very similar images in capture time order). Scenes will load in after the initial project creation and may take a minute or two to appear. Here's what you can do with scenes:
Navigate straight to the first image in the next or previous scene by pressing ←/→ (arrow keys can be swapped in Preferences)
You can cycle through all the images in a single scene by pressing ⌘ + ↑ / ↓ (mac) or Ctrl + ↑ / ↓ (windows)
You can hold ⌘ + shift and click on a thumbnail (mac) or ctrl + shift + click (windows) – all images in the scene will be selected.