Setting up the Asset Library

Step 1:

Unzip the downloaded file and move the contained folder with all files (i.e. .blend as well as the thumbnail folder and other files that contain the catalog structure for the asset browser) to a storage location of your choice.

Step 2:

Set the whole folder, containing all files, as your asset library path.

Edit -> Preferences -> File Paths -> under Asset Libraries add a new file path by clicking the + icon.

Step 3:

Open a new window in Blender and select the Asset Browser as your workspace. If the file path is correct, you should be able to see the new catalog with the Bridges and Pathways subcategories!

How to use:

Simply drag the assets from the asset browser into the 3D viewport and the model should be created!

You probably don't want to use the presets, so just switch to edit mode and delete all vertices by pressing X on the keyboard. In the left toolbar, which you can expand by pressing the T key, select the draw tool.
Now you can easily draw curves however and wherever you want!

Pro tip:

Switch the drawing mode from Cursor to Surface. The curves should now stick to the surface underneath it!