Lenny, Let me explain how our system works.
When visitors open the website the system will show the page listed at the first position in the main menu. I.e. if the first menu item is the Main, the system will be load the content of Main page as though it the index page. But if, for example, you will place the Members menu item on the first position, then visitors open the website will see the content of the Members page as the index page content, wherein url will be http://sitename.com/ but not the http: // sitename.com/users .
The index page has its own route http://sitename.com/index by default but when it listed as first in the Main menu according to rule of our routing system when you open your site you will see http://sitename.com / .

We can suggest you a few options how to avoid duplicate content:
First- you can create custom page with some content and place it as a first page in Main Menu.

Second- change .htaccess file by adding 301 redirect. You need to paste these lines after all conditions in the end of file:
RewriteCond %{REQUEST_URI} /index$ [NC]
RewriteRule ^(.*)$ http://example\.com\/ [R=301,L]

P.S. If you are using the second version the Main link must be the first in Main menu.

Hi Taissa,

Thanks for your explanation.

I used the second options, it works fine !

Lenny

and how to make the join page to be first, if your site isn't closed for guests ? 

DeFender, all you need is just to place  the Join button at the first position in the main menu.
You can do it in the Admin Area>Pages&Menus> Pages&Menus section. Drag the needed menu item and drop it at the first position.

If you are  referring to changing the .htaccess,  paste these lines after all conditions in the end of file:

RewriteCond %{REQUEST_URI} /join$ [NC]
RewriteRule ^(.*)$ http://example\.com\/ [R=301,L]

thank you I know it, but I want if a site is visible for the guests, but typing www.example.com it redirects to join page, like site is closed for guests. sorry for my english :)

remove the join page from first spot in admin pages 

it is not working :(

maybe Im not right by saying join page, I want login or sign up  page when the site is visible by guests.

Please see this topic: http://www.oxwall.org/forum/topic/14261
If I took you wrong - please provide me with more details.

new start :)

site is opened for guests.

how to get this (maybe it is javascript) when typing example.com or example.com/index

(My site is not using index page)

DeFender, if you want to set your Oxwall Sign-in Page as the landing page without disabling the site for guests, then you can use this solution: http://www.ewtnet.com/...sign-in-page-as.html

vielen Dank Taissa. ;)