This toolbar consists of the following actions. Clicking at an action means that your mouse pointer applies this action at the graph editor whiteboard:
Select and Move: To select elements, either click at unused space at the whiteboard, keep the mouse pressed and draw a rectangle that contains some data elements and/or edges to select these elements or otherwise directly click at an unselected element to select this element. If you click at a selected element or a set of selected elements, respectively, by keeping the mouse pressed and moving around you can move these elements. Moving selected elements is also possible with the arrow keys.
Create Node: Click at an arbitrary position at the graph editor whiteboard to create a new data element that belongs to the currently selected data structure. By keeping the mouse pointer pressed at the button, a menu shows up at which the data type of the new created data elements can be selected (only if different data types exist).
Create Edge: Click at one data element, keep the mouse pressed and draw a line to another data element to which the edge shall point. This action is only successful if the current graph allows to add this edge (e.g., in an undirected graph you are not allowed to add multiple edges between two data elements). By keeping the mouse pointer pressed at the button, a menu shows up at which the edge type of the new created edges can be selected (only if different edge types exist).
Delete: Click at an element to delete it. If you delete a node, all adjacent edges are also deleted.