Autodesk Dynamo for Civil 3D is a visual programming application that you can use to automate tasks in Civil 3D.
Autodesk Dynamo for Civil 3D is available as a separate installation for Autodesk Civil 3D 2020 through the Autodesk Desktop App and from your Autodesk Account.
After you install the application, the Dynamo-related commands are available on the Manage ribbon tab in Civil 3D.
On the Dynamo Start page, these samples are listed in the Samples section:
To use the samples, open the drawing that is associated with the script and then run the script. You can open the script in the Dynamo editor to review it and run it, and you can also run the script by using the Dynamo Player.
For more information about the samples, see Samples for Autodesk Dynamo for Civil 3D.