Questions

The ones that actually get asked

Can I start numbering from the second page?: Yes, and that is the usual choice when the first sheet is a cover.
Will the number show in print?: Yes. It is part of the page rather than a counter in the program you open it with.
What about a document assembled from several files?: Number it after assembling — then the whole thing gets one shared run.
Is the document uploaded to a server?: No. Numbering runs in the browser.
Can a number be changed after adding?: The numbers are part of the pages, so a correction means numbering the source document again.
What if I do not want to continue?: Cancel from the account in two clicks; there is also a cancel page without a login.