Hi,
To insert a image drag it onto the page, or from the Pages menu click Insert / Choose, select the image you want to add to the document and then click insert. You can then use the inspector to change and create how you want the text to flow around the image.
Re the header box, just tab return and the curser will drop below it, have to say I am a real pages fan, you can create absolutely stunning documents.
Hope I have fully understood what you wanted to know.