The guys above got it covered 100%. If the first target is a ship, get within 600m of the ship, if it's a Station you have to dock.
When the requests are completed Comms will get a message.
Example Scenario:
Sub-mission start
"DS3: Artemis, gather supplies from Tr37 and return to DS3 and we will double our production speed."
Artemis < 600m from Tr37: "Tr37: Artemis, return the supplies to DS3 and they will double their productions speed."
Artemis docks with DS3: "DS3: Thank you Artemis, doubling our production speed as promised."
End sub-mission.
Side note relating to Comms:
If the Captain gives a damn about the Transports and Destroyers Comms should stay plenty busy during any mission rerouting those vessels. But in general scenarios (Siege, Single Front, etc.) Comms does have plenty of play room.