Changes to the structure of your document should be made on the Master pages. By default, a single sided document will only have a master page title "Right". A double-sided document would then have a "Right" and a "Left" master page. You can add as many master pages as you need for a document, however when you are writing text and come to the end of a page, by default Frame will create a new page using the format from the left or right master page.
You should think of the master page as including any information that you need for any and all pages of a single format. This would include headers/footers and the layout of the text on a page (for instance, the margins, or number of columns on a page).
Once the changes to a master page are made, they may need to be applied to the appropriate body pages in your document. You should only explicitly change a body page if you know that the change is only for that page, and that any changes to the document are not going to require those changes be undone.
In the body pages you should only include the body of the document, such as any text, figures, tables, etc. that you may need to include. Since these are generally not duplicated, there is no need to place the information on a master page.