how can i make a helpline on every page and everytime in the same location; must be easy, but i cannot find it

You need to edit the layout, then apply that across the book.

See the iBA user video in iTunes Connect and see: Publishing With iBooks Author

Make sure that the Show Layouts panel is visible and use it to edit the template. It's fairly straightforward. Just make sure that you click the Apply Changes button when you're done - all chapters/sections/pages in your iBook that use the template part you edited will be automatically updated.