To create a Custom Catalog, go to the 'Custom Catalog' widget in the Dashboard and click the 'New' button in the top right corner:
This brings you to a page where you will create a new custom catalog:
You can give your custom catalog a name (this will make it easier to find later). A custom catalog is your own workbook of selected styles and colors from a base catalog. Select the base catalog you would like to work in and click 'Create'. This will open up the Custom Catalog Builder and you can start building your assortment.