Facebook – Can’t rearrange open chat tabs anymore

Indeed, Facebook has stopped Import notes feature:

We want you to connect with your fans in the most effective ways possible. That's why as of September 30th you'll no longer be able to automatically import posts from your website to your Page notes. The best way to get people to interact with your content is to give them insight into the links you share on your Wall by adding personal comments and responding to feedback from fans.

We're focused on creating even better tools for Pages. Look for announcements soon.

Are you trying to develop your own app, or adding an app that has already been written?

If you go to an existing app that is intended to be added to a page tab, it will usually have a button/link to add the app to your page. If you click on this a dialog should pop up and let you choose the page, from the pages where you are an admin.

If you have written your own app, or the app does not have an Add to Page link, these instructions on the Facebook Developers site show how this link can be added to your app or entered manually. If you want to enter it manually you can copy and paste the following URL to your address bar: https://www.facebook.com/dialog/pagetab?app_id=APP_ID&next=https://www.facebook.com/connect/login_success.html (Change APP_ID to the app id you want to add. The app id is a number which can be found in your app settings, or in the URL for the tab if it has been added to another page.)

If you want to develop your own app but haven't yet done so, go to the Facebook Developers site and check out the Page Tab Tutorial. Then add your new app to your page using the above instructions.