To add the selected photos to a category, just type the first few letters of the category's name in the status bar. You'll see a list of matching categories as you type. You can choose a category by clicking it, or selecting it with the arrow keys and hitting return.
If there isn't a category with the name that you've typed, Shoebox can create a new category for you automatically. In the Categories preferences, you can choose whether Shoebox should create a new unfiled category, ask where to create it, or do nothing.
You can also select a category in the Categories window and choose Categories ▶ Add Photos. Hold down the option key to add all the displayed photos.
You can also click the button next to a category in the Categories outline.
Shoebox remembers the most recent category that you've added a picture to. To add another photo to that category, choose Photos ▶ Categories ▶ Add to “Recent Category” (⌘').
If you have two pictures in a row that belong in the same categories, you can choose Photos ▶ Categories ▶ Add to Same Categories as Previous Photo (⌘"). The selected photo will be added to all the categories that the previous photo is in.
You can also copy and paste categories. To copy all the categories of the selected photo, choose Edit ▶ Categories ▶ Copy Categories (⎇⌘C). You can then paste them onto the other photos.
You can also drag photos to categories, or drag categories to photos.
To remove the selected photos from a category, select a category and choose Categories ▶ Remove Photos. Hold down the option key to remove all the displayed photos.
You can also click a category in the status bar and hit the delete key.
You can also click the button next to a category in the Info window.
To remove the selected photos from all their categories, choose Photos ▶ Remove from Catalog.