This Icon  takes you to the Manage Product Categories tool.

NOTE: Press and hold the CTRL Key down to select multiple Categories from the list below.

WARNING: Be sure you press and hold the CTRL key BEFORE you select any new categories to retain the categories that this product is already assigned to. If you do not hold down the CTRL key before selecting any categories, you will remove any already assigned categories…

For more information see Working with Type and Theme Categories