Are you asking how to add widget to content_bottom widget are?
Then you can follow http://classibase.com/how-to-display-subcategories-on-category-page/ this tutorial or in short follow these steps.
- Navigate to Appearance -> Widgets on “Admin panel”
- Open “Content bottom” widget area at the bottom rigth of page.
- Drag “Text” widget from “Available widgets” to “Content bottom” widget area with your mouse.
- Click on edit next to Text widget, popup window will open.
- Put text you want to display. Also if you want to use HTML or PHP select appropriate text type from select box below text area.
- Also tick pages on which you do not want to display current text widget.
- Click “Save” button and check your website for changes.
If this is not what you asked, then please clarify and let me know.