There are a handful of escort missions in Fallout 4, but none quite as adorable as this. After completing A Loose End, Captain Kells will start offering this repeatable quest. You'll first have to rendezvous with a Brotherhood Squire at Boston Airport.
You're in this mission to show her the ropes by taking on hostiles in a randomly designated location in The Commonwealth. One such place is College Square Station. Kill all the targets as indicated by the waypoints.
Talk to the Squire upon completing that objective. Then return to the Prydwen to give Captain Kells your report and finish the quest.