The Transition Editor is intended to be used when playing simulation in Line Simulation (LS) mode (cyclic simulation).
In standard mode when two operations are linked, one will start immidiately when the previous one ends.
In LS mode in addition to the link there is also a condition that must be fulfilled before the 2nd operation can start. So when an operation ends, simulation evaulates the condition described in the Transition Editor. If this condition is TRUE -> the 2nd operation will start. If it is FALSE -> the operation will wait until the condition is met.
This is just a short explanation. You can find further infromation in the Tecnomatix Help under topics such as "Transition Editor" or "Sequence Editor with Line Simulation Add-on".