Twilight, as an alicorn, now has both pegasus and earth pony magic in addition to her well-practiced unicorn abilities. However, she has little idea how to use these abilities, and thus seeks tutors.
Applejack and Big Mac are busy with the zapapple harvest. Granny Smith tends to nap in the afternoons. And Pinkie Pie is... well, Pinkie Pie.
Fortunately, there's an Earth Pony with a free afternoon who's willing to give teaching a try... especially if it might lead to a cutie mark...