The machine is constructed by the graphic editor. You select the needed elements out of a list, place them in the graphic window and edit their properties.
Then you start the simulation with the symbol 
. While the simulation is running (green light on the bottom left) you cannot edit. The stopping of the machine with the symbol 
is equivalent to the switching to the edit mode. You can stop a simulation run for editing as many times as you like. After restarting the simulation will be resumed at the point where it is interrupted.