to the tpo page of the manual

Divide a Line

If the mouse cursor is moved to over a selected line, shears mark appears.
Right click at where you want to divide line, and select "AddNode".
How to delete a node
If length od a line becomes zero, the line is deleted automatically.

To delete node "A".
(1)Select the Selector tool
(2)Drag to create a rectangle to enclose node "A".
(3)Drag node "A" to the next node or the end of the line.