I am an engineer who works in the field, commissioning equipment.
Commissioning is the process where everything associated with the equipment is fully checked, all items are simulated or caused to happen, all possible events are tested, all methods of failure are accounted for. In other words, the complete design of the equipment is tested. Then, and only then, equipment is run and shown to be according to the design.
This is commissioning.
You could put equipment into operation without fully checking all systems. You can just run equipment and hope that all safety systems work according to plan.
That is the difference. No manufacturer or reputable engineering firm would simply put equipment into operation.