How can I move a page to become the child page of a different page

[Richard Hancock]

How can I move a page to become the child page of a different page

[Andrew Dildy]

@Richard Hancock assuming the pages are in the same page tree, you can simply drag and drop pages to reorder them directly from the page tree.

As mentioned in other answers, the ••• > Move dialog can also be useful, but is really only necessary if you are moving pages between spaces.

[Nic Brough -Adaptavist-]

You can use "move" from the tools menu at the top right of the page (the ...) or you can go into "space admin", find the content tab and get a page tree, within which you can drag and drop pages

[Bill Bailey]

Select ••• > Move.  The Move page dialog box appears.

Here is the doc page https://support.atlassian.com/confluence-cloud/docs/move-copy-and-hide-pages/