Creating a page: what you need to begin
A name and a main photo. Everything else — dates, a nickname, the story, the people — can be added any time.
Say whether the page is about a person or a pet. Then a name and a main photo are enough; the dates of their birth and passing sit beside them, and both can wait. You can add a nickname, a hometown and a short story now or later.
The main photo
Under the photo, one choice: Fill or Whole. Fill makes the photo the page's band, cropped around the point you pick, with the name over it. Whole shows every pixel — nothing cropped, the name under it — for a landscape or a group shot. A wide photo starts as Whole, a portrait as Fill; switch any time under Settings → Details.
After the page exists
Start with one memory — a story, a photo, a moment. Then invite the people who were there; the page grows from what they add. Life events, occasions and the people in their life are kept under Settings, so there is one true answer for each fact. See Memory or record?.
Who can see it at first
A new page is for you and the people you invite — nobody else can open it, whatever they type. One switch under Settings → Privacy lets anyone with the link read it (read, not add), and nothing is public until you choose that. See Who can read the page.