A namespace is identified by having a colon after its name:
id=namespace:
Or if you have the useslash configuration option set set to true:
id=namespace/
The same principle would apply if you were using nice urls, for instance:
doku.php/other_ns/
which would translate to:
doku.php/other_ns/start
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Edit:
start is just the default page name. Normally, you would create pages with their own identities and link to them either through a menu or the sitemap or with links inserted into your pages. You can also find templates with sidebars that give you the option of creating in effect indexes from which to link to your pages.