Categories are a means of grouping similar items together in SOS Inventory. SOS Inventory supports up to three levels of categories (a main category and two subcategories). This mimics the limitation of categories in QuickBooks Online.
As an example, if a company carries a variety of chairs, the chair inventory items are scattered throughout the Items list. However, if you create a category called Chairs and assign all chair inventory items to that category, you can use the Filter or Quick search feature on the Items list to limit the items displayed to items assigned to the category Chairs.
Some reports and data exports pertaining to items have the option to filter results by category.
A category, whether a main category or a subcategory, is classified as a Category type item in SOS Inventory. Both categories and subcategories are created using an item Edit page. (However, categories and subcategories can be created in QuickBooks Online as well.)
The graphic below illustrates the creation of a category item named Produce using the above steps.

The new category will appear in the Items list and will be added to the dropdown list of choices for the Category field on an item Edit page.
To assign an item to a category, create a new or open an existing item on the Items list. For each new or existing item that will be assigned to that category, select the name of the appropriate category from the Category field’s dropdown list. In the screenshot below, the item Blackberries has been assigned to the category Produce.

In transactions, you can search for the Blackberries item either by its name or the category Produce.
Please note that the structure of the category names will always be separated by a colon. In the example above, the item's full name would be displayed as Produce:Blackberries. It is good practice to keep category names short due to the full name being limited to 100 characters.
In addition to the main category, you can assign items to a subcategory. If you are using two levels of subcategories, the higher-level subcategory is the parent of the lower-level subcategory.
Using the Blackberries item above as an example, you might want to have that item's category more specifically defined than just Produce. Keeping Produce as the main category, you could add two levels of subcategories: a subcategory of Produce called Fruit, and a subcategory of Fruit called Berries.
When creating these subcategories, note the following:

When you assign a category to the inventory item Blackberries, the options Produce, Produce:Fruit, and Produce:Fruit:Berries are displayed in the Category field drop-down list. You can now assign Blackberries to your desired category, Produce:Fruit:Berries.

In this example, the item's full name would be displayed as Produce:Fruit:Berries:Blackberries.
You can use both the Quick search and Filter features with categories, but they have different capabilities. Quick searches will return more records, especially if you use categories. You may prefer to use one over the other, depending on the data you want to see.
For example, a quick search of Produce on the Items list displays the following. When the Type, Category, and Full name columns are enabled, the main category (Produce), both of its subcategories (Fruit and Berries), and all associated inventory items with that category structure (Blackberries and Raspberries) will be displayed.

However, if all you want to see are the inventory items associated with a specific subcategory, you may prefer to filter by Type (Inventory Item) and Category (such as Produce:Fruit:Berries) instead of typing the category string (Produce:Fruit:Berries) in a quick search.