It's just guide lines, they will not show up in your final product. (Well ... unless you happen to have checked "Include Guides" on exporting to PDF.) Switching to "Preview" mode will hide them from view.
You can safely ignore them, for anything you are designing. Just pretend they are not there. If you find objects are snapping to these guides (which is one of their primary functions), toggle off "Snap to Guides".
You can't switch them off *entirely*. You can set the number of columns to "1" (it seems to be set to "4" here), but you'd still have the *outer* guides, indicating the default text margins for your document. You can set these margins to "0" , but then the purple lines are drawn on top of the actual page border, which may still be somewhat distracting.
Thanks a lot!
You can't switch them off *entirely*.
But you CAN hide them. Ctrl + ; or Cmd + ; (depending on the platform) is the default keyboard shortcut to toggle guide visibility, and you 'll find it in the View menu, too. They also disappear in Preview mode.