To add a Node, click on the surface, name it, and press Enter. You can change the location of a Node by dragging it to another place and dropping it. However, note that you cannot remove a Node anymore, once it has been added.
To connect 2 Nodes, first click on one of the Nodes you want to connect, then click on the other node with the right mouse button.
To attach a file, click with the right mouse button and choose a file. In this way, you can also download attached files.