When you use a standard collection view, it uses a grid layout. In this grid layout, all items are evenly spaced, and all items have the same size. You can visualize this quite easily by giving the collection view cell a background color in your Storyboard and running your app. This standard grid layout makes adding a grid to your app a breeze. However, the standard implementation of the grid layout is not quite perfect. If you look at the grid you have set up, it should look good on, for instance, an iPhone 8 but when switching to a smaller screen such as the iPhone SE, the layout looks nothing like the beautiful grid layout you saw before. Viewing the grid on a larger screen such as an iPhone 8 Plus doesn't make it any better either. The grid would be significantly improved if every cell was sized based on the size of the screen. Let's see how this can be achieved.
In your storyboard, select the Collection View Flow Layout object...