Every Tuesday, the teacher's small, pudgy fingers hopped about across the piano keys like a bird.
Literal
Every-week Tuesday [topic-には], teacher [possessive-の] round-and-round small fingers [subject-が] piano [possessive-の] keyboard [object-を] here-and-there [manner-と] bird [like-のように] was-hopping.
ころころした is a 擬態語 (state mimetic) for something round, small, and plump — here describing chubby fingers. あちこちと ('here and there') marks the scattered, flitting movement. 飛びはねる ('hop about, bounce') is a compound verb: 飛ぶ ('fly') + はねる ('bounce'). The simile 鳥のように ('like a bird') completes a vivid, literary image.