In Open Office, go to Format/Page/Header to assign attributes to the header. Your description implies that you'd want to check "Header On" and "Same Content Left and Right" but there are other attributes you can set as well. When you are finished and click on "OK" your blank page will have a rectangle at the top for filling in your header text.
Assuming you'd like your page number in the header, tab or space to where you'd like the number, then click on Insert/Field/Page Number. The page number will appear in the header and the header and page number will repeat on subsequent pages.

BTW, I'm using OO version 3.2.0, but I don't think this procedure has changed lately.