Hi Kat! I've ghostwritten both fiction and autobiography, so far, but Upwork is a new experiment for me – I tried it in the past and found most "clients" were just trying to pay pennies, but giving it another try to see... (The job I'm posting about is editorial work.)
When you submit a proposal to the job you state your desirable rate or budget. However, you may then discuss the project with the client further during the interview and the terms may change.
When the client sends the contract offer, they state the finalized terms, amounts and deadlines as well as create and fund milestones. You then need to accept the offer if you agree to those terms or decline it if you disagree. When you accept the offer, check if the client funded Escrow for the amount you both previously agreed to.