How to setup the oauth module? I don't know how to setup the outh module right. I found also the question How do I configure the Services OAuth sub-module? but that answer is very old and ends with a "To be continued..." statement.

So far I get out that I need to generate a context (http://example.org/admin/config/services/oauth/contexts) and a oauth connector (http://example.org/admin/structure/oauthconnector). So I think I setted them correctly but I cannot see where the user may access that.

Could you point me to a tutorial or something like that? I'm not able to find the right words to google that myself. Sorry for that!
You can try the Drupal Services, REST Server and 3-legged OAuth tutorial here. Just be pay intention in this part :

$oauth-&gt;fetch("$api_url/node/1");


This is just for creating the GET request. If you want to create the POST request. It should be something like.

 $oauth-&gt;fetch("$api_url/user/vote.json",array('nid'=&gt;10),OAUTH_HTTP_METHOD_POST);