If you have the Power Add-on ( Tagalong Legacy documentation is on home site old docs page) you will see a header tab in your Store Locator Plus menu labeled Categories. This is where you can establish and manage settings and determine the categories you want to add in the form section of the user interface. The two sub sections under Categories is Settings and Taxonomy.
Settings determines what you want to be displayed on your site page to the public. The term Taxonomy references the WordPress category system and where you will set up your category hierarchy and markers.
Additional features for Categories with built-in complex logic for parent /child drop-downs to be displayed in your search form are available only with the Premier subscription. A tutorial video on the SLP YouTube Channel is available for this additional feature with premier.
Taxonomy is where you establish and manage the categories themselves.