The proposal describes your dream project. The proposal is your opportunity to detail the scope of your project, its context, what you need to make this happen, your timeline and milestones, who are your teammates if you have teammates, or if you are planning to proceed individually.
In the first deliverable, it does not need to be a fully formed proposal but a rough first draft. There’s no specific page requirement, but 4 to 8 pages of text total, or perhaps 10+ PowerPoint slides might be a good length.