The widget allows you to add or create various listing options, such as conditions, body, makes, mileage, model, fuel type, etc.
To add an option item, you need to click on the preferred one from the left group of the windows, and the chosen option will appear in the Selected group of windows.
To create a new option item, choose the window from the right group of windows and click on Add new, write down the name of the new option, and press the + button.
If you want to unselect the item, just click on it, and it'll appear in the opposite window.