This is the basic of viewing our photos in Adobe Lightroom, the Grid View and Loupe View. You might want to try the shortcut key for both veiwing mode, to view the photos in grid view, press G (both Windows & Mac).
You can adjust the increase/decrease thumbnail size by pressing “=” (increase) or “-” (decrease) – it work for both Windows & Mac.
If you want to view it more detail and bigger, press E (Loupe View).
You can actually expand Loupe view by hiding the side panels, filmstrip, module picker, and expand it to fullscreen viewing. Shortcut key for this is Ctrl + Shift + F (Windows) and Command + Shift + F (Mac)