Thank you for your message. Milestones are a way to divide the fixed-price job into a series of deliverables based on your needs. They can break a larger contract into more manageable chunks. Freelancer and client should discuss and agree upon all milestone amounts, deliverables, and deadlines prior to beginning work. For more information about milestones, you can check this help article. You can also propose changes to already existing milestones or propose new milestones.