Go to your page types and click on "defaults." Once you add it to "defaults", click on the block you just added. You should see "Setup on Child Pages" as an option.

If you select this you should see a list of all pages in your site that share this page type. Then there are check boxes that show which pages of this type this block shows up on. Select all the pages using the check box in the header, or select individual pages, and click save. The block should then be aliased out to those pages.

Changing the block in the "defaults" section should then propagate its changes out to all the ones you've selected (as well as automatically be added to new pages of that type.) If you change the block on any of the child pages, it'll override those settings and create a new instance of the block.

As an altertnative you can also use the scrapbook feature, where you can reuse a piece of content in different areas in your website.

http://www.concrete5.org/help/using_concrete5/how-tos/scrapbook_defaults/

I saw the video tutorial, but when i click on "default" to set my page as default, it opens a new C5 login window !
So impossible for me to set default page...

I'm running french localized C5 version, could it be the problem ?

Thanks...