The Elements Window is the place to find and add the nodes available in Cavalry.
To add nodes to your scene simply drag a node from the Elements Window into the Project Window.
You can use the search bar at the top to filter the results or use the tabs to filter based on the type of node you're looking for.
You can also add nodes via the shortcut at the top of the Scene Window (+ sign).
To add nodes you can either:
Double click on a node.
Drag a node into the Scene Window.
Use the down/up keys to select a node. Hit enter to add the selected node.