[Muellmann]

To enable avatars just ensure this setting:

In Admin Control Panel (ACP):
vBulletin Options->User Picture Options->Avatars enabled->Yes

Avatars->User Picture Storage Type (leave the default settings)
Avatar File Path: ./customavatars
URL to avatars: customavatars

Ensure that a folder "customavatars" exists in your forumroot,
usually "forum/customavatars"

Chmod this folder to "777" with your FTP program if there are no permissions
to write in the directory.

in your usergroupsettings in the "Usergroup Manager" in ACP should be for each group (usually registered users moderators and administrators) the privilege "Can Upload Custom Avatars" set to yes.

Also these should be not "0" - example settings

Custom Avatar Maximum Width (pixels) 100
Custom Avatar Maximum Height (pixels) 100
Custom Avatar Maximum File Size (bytes) 25000

With "Avatars->Add New Avatars" in ACP
you can add a few own default avatars

For including a referral link to free avatars you should do a template edit.
If you need more help you can ask me again.