I have installed subdomains and I did all 3 steps:

STEP 1: Set the $cookie_domain variable in your settings.php file to your site's domain (e.g. $cookie_domain = ".example.com")

STEP 2: Enable wildcard DNS on your DNS hosting provider (e.g. *.example.com)

STEP 3: Configure your webserver for wildcard virtual hosts. (HINT for apache: ServerAlias *.example.com)

STEP 4: Enable this module and configure

NO ERROR when I go to Subdomain Settings.

but if I go to username.mydomainname.com it shows all the articles from all user (it should show only the content posted by that user). also if I go to userthatdoesnotexit.mydomainname.com it show me the same index page but the users does not exit.should redirect me to page not found or something.I can type even abs.mydomainname.com still the index. it does not make sense.abs.mydomainname.com does not exit. If I go in user account there is no link in this account or profile to his on subdomain.

I enabled clean urls.still nothing. I added in Subdomain Settings-filters-Drupal path-Blacklist- article (added even article/* ) if I type nothing is the blacklist then username.mydomainname.com redirects to http://mydomainname.com/node

I don't know how to set up filters.I have clean urls on.