By default game has only one shortcut leading to singleplayer mode. To get to multiplayer you have to run first singleplayer and from this switch to multiplayer. You can easily run multiplayer directly, create shortcut and paste into it this:
<pre class="ip-ubbcode-code-pre"> "C:\Program Files (x86)\Ubisoft\Assassin's Creed Revelations\ACRMP.exe" /launchedfromotherexec /onlineUser:***** /onlinePassword:******* </pre>
This example is for default path in x64 editions of windows'. Instead of stars type your username and password.