Add transition by marking the rectangle tool on toolbar and clicking at the canvas to spot, where you want to place the transition.
Perform double click to open the properties window of the transition.
Properties ID, Name and Color are available for every type of nets. The transition function is allowed only for Time/Basic nets. Editing of these is allowed only at specific types of Petri nets. If you want to cancel the addition of transitions, just unmark it's icon on toolbar.