Categories are something you assign to recipes. You can assign them to your online recipes or from MasterCook on the computer.
Go to your My Recipes web page here:
Click on one of your recipes to open it. Click on the Edit link just below the recipe's title. At the bottom of the recipe edit screen, you can assign an existing category.
In MasterCook on the computer, you store recipes in cookbooks, just like in real, published cookbooks at a bookstore. Within a cookbook, you can assign categories to the recipe. To assign or change a category of a recipe, open the recipe in the recipe edit screen and use the Categories tab.
If you open a cookbook so you are looking at the recipe titles, along the left of the screen you can select to Sort Recipes By: Categories. Just above that, you can press the Categorize button. This is an additional way to categorize your recipes. You can select multiple recipe titles in this screen and categorize several recipes at once.