Select the Firearms folder and click Ins to create an entry under Firearms and name it “Rifles.” Do not enter any data. Be sure to hit return after typing the new name and then click the Save button to save it.
Using the same approach Create folders for “Shotguns,” “Pistols,” and whatever sub-categories you wish to group items by.
Add an initial item for each one by selecting the folder and clicking the “Ins” button. You can even add sub categories using the same method descriped above as illustrated below:
Now you can continue to create new items and/or drag and drop any existing items to the new folders.