Transport
Floo Network
The Floo Network connects wizarding fireplaces. A traveler throws down Floo powder, steps into the green flames, and states the destination clearly. Harry’s first trip, from the Burrow, goes wrong and drops him in Knockturn Alley. The Ministry’s visitor entrance and many home fires are on the same network, which the Ministry can watch.

First mention
Harry Potter and the Chamber of SecretsChapter: At Flourish and Blotts
The Weasleys leave the Burrow by Floo powder for Diagon Alley. Harry muffs the destination and arrives in Borgin and Burkes.