A crucial and very important part of your store are your product and collection pages. There are global settings that affect both in this tab.
Most notably, you can change the aspect ratio for your product grid to make the blocks wider, taller, or square (1:1)
You can set the image to stretch across the block or to render itself in full inside of it. The latter can result in extra white spaces while the former could cut parts off. The most important thing here is to set the proper aspect ratio.
Another great option tucked away under this tab is the 'products per row'. This is split into two different settings, one for mobile and one for desktop.
Remember, these are global settings so they will affect all pages.
To give an example, your collection page grid is linked to these settings and so is your featured collection section on the home page.
Color Swatches can be toggled here too. This feature can often require additional work to be fully set up. Modular can recognize a few custom color names but not all.
We highly recommend checking out our full-length post on the topic of Color Swatches.