To add a new node, click on empty space in the canvas. Use the dialog box that pops up to set the node's value to either a type or an entity.
To add a new edge between two nodes, hold down the shift key, click on one node and drag to the other node. Select the edge value from the dialog box that pops up.
To re-position a node, click and drag the node around.
To remove a node, select the node by clicking on it and press the Delete button.
To edit a node's value, double click on the node and use the dialog box that pops up to change the value.
To remove an edge, select the edge by clicking on it and press the Delete button.
When the Reverse Role button is displayed in the Edge Types/Reverse Role panel, clicking on it reverses the role of the two ends of the selected edge.
When the Add Edge button is displayed in the Edge Types/Reverse Role panel, click on it to add two new grey edge instances of the selected edge, one on each node of the edge's ends.