The younger one has taught herself almost everything the older one knows, mostly by observing him, but sometimes by him actively trying to teach her. When she doesn't know something, he shows obvious signs of frustration and urging: I give a command, he does the thing I'm asking for, she doesn't react because she doesn't know the command, and then he starts growling and harumphing (and sometimes even air snaps near her face to get her attention) until she follows his lead.
You can train herding by simply stopping the herding when he messes up (negative punishment). As long as he does it correctly he keeps doing it (positive reinforcement).
For my border collie it's similar in agility. He doesn't care about treats and barely needs toys - doing the agility is the reward for learning it for him