From web page oneminuteinfo
Let's assume you need to display an article site wide, at some position of the template. Then you'd like to be able to edit it from the frontend administration panel. This means you want your frontend admins to be able to edit the content without your need to get involved. You do NOT want your frontend admins to need to log into the backend admin panel to do it.
You can create a custom HTML module and put it in some position of the template. However Joomla does NOT allow a frontend admin to edit a module! How strange is that! To add insult to injury Joomla does NOT allow a module to point to a single article!
Step 1: You need to link a module to an article you'd like to allow frontend admins to edit.
I find it annoying that Joomla does NOT allow a module to be linked to one article. However it allows a module to be linked to a category. This is where you can exploit a workaround.
Simply create a category and put one article in it, and create a module (type Articles - Newsflash) to point to that category. This is an easy workaround to link a module to one single article. Just remember to NEVER add any more article to that category.
Configure this module so that it appears in the desired position of your template.
Step 2: You need to create a menu item linked to that article with correct access setting.
Go to Menus -> (whatever your main menu is called) -> Add New Menu Item. Pick 'Articles >> Single Article' for Menu Item Type. Then select the correct article for this menu item. Then select 'Registered' in the Access drop down menu.
If you are having difficulty getting this to work consult the following tips:
1. If you don't want to display the article title, then edit this Newsflash module, pick 'Hide' for 'Show Title' in 'Details' section. If your article contains images you need to pick 'Yes' for 'Show Images' in 'Basic Options' section.
2. Make sure the frontend admin belongs to the user groups for Registered. Suppose the frontend admin has been assigned to 'Publisher' user group. This means when you go to Users -> Access Levels and click on Registered you'll see check box of at least one of the following checked: