You can use a tool catalog item in Autodesk Civil 3D by dragging a tool directly into the drawing area from the Content Browser. For example, with the Getting Started Subassembly catalog open, drag the BasicBarrier subassembly into the drawing area by clicking on the i-drop icon, and dragging it into your drawing.
You can also drag a tool catalog item into the software’s workspace, which adds the tool palette to the default tool palette set. For tools you will use frequently, save time by adding the tool to a palette in the tool palette set, where you can access it without using the Content Browser. Once added to the tool palette set, the palette remains a part of the set and is available each time you start Autodesk Civil 3D.