In Site -> Referrers you can define filter for web site referrers which you can use to track how your visitors get to your site.
We are using the same tag mechanism as Google Analytics. Check
here for the some explanation. You can put any regular expression in "Medium Match String" which run against the value that is specified in "Medium Match Target". The following example is used to identifiy the Google CPC tranfic.
| google |
gclid= |
Landing URL |
cpc |
gclid= |
Landing URL |