Type some text in the navigation bar, the module will search on DuckDuckGo and display some results.
This module is NOT an official module from DuckDuckGo.com however it uses DuckDuckGo's public API.
Open the module manager (right click + "configure module"), in the "Install modules" textbox add the following and click install.
github:http-teapot/mod_duckduckgo
Once you click "install" the module will be added to the table above; you will need to wait a little bit for it to install and then you are good to go.
For more information, refer to the LICENSE file in this repository.