The Question and Answer section for A Tale of Two Cities is a great resource to ask questions, find answers, and discuss the novel.
The footsteps are the advent of revolution, the footsteps of an ideal. This line is not meant to be taken literally, it is symbolic.
The lumber and carts refer to the tumbrils (wooden carts used to carry prisoners to the guillotine) on their way to punish the criminals.
Dr. Manette believes he learned to make shoes in prison.