He learns it the way he always has learned ever since he became captain to the Enterprise, and this is the way he now divides his life: before she became his and after.
Yes, he learns on a learning curve steep enough to fall off if he makes the slightest misstep, which he seldom does, and even if, even if, then Spock is there to pull him back up. Learning loudly and boldly into the darkness but never alone, not with his crew and Spock behind him, one pace, a hand that will rest slightly on his shoulder when he falters. In long lit alpha-shifts when they debate over nothing and switch sides of an argument as easily as a coin can be flipped, in shore leaves and strange sights they show to each other, in the heat of the battle and the flash of the phasers but more often in peace, when he goes into Spock's room or Spock into his, and perhaps they play chess or sit in silence and enjoy that their lives have been brought together, lax and content in a way he had never thought possible before.
He has heard himself called an unstoppable force and Spock the immovable object, well, for Spock he stops moving and for him Spock gives way, but neither is necessary, neither asks it, for they are past it now and have been for a long time, maybe forever. Learning and teaching and letting himself be taught, when he thought he could accept no teacher.
Learning, and the lesson is love, and it may just be the most important thing he'll ever try to learn or ever try to be taught.