The Schema Library is a collection of predefined database schemas for a wide array of industries. You can immediately use these schemas, or adopt and modify them to suit your purpose.
The section on the left shows the different categories/industries you can pick from, and as you select a category, you will see all the available schemas for the category.
Further to the right, you see the graphical representation of the schema. If you want to zoom in, you can click the "Image Zoom" button: