As we mentioned before, when someone finds your site via a link on a social network, they'll be bucketed under social media as a traffic source. This could include someone tweeting out a link, or it could include you posting a link to your Facebook page. If it's you doing the posting, you can also add a tracking token before posting to track those links as part of a larger campaign for you to analyze later!
Once you've set up an alert within Mention, go to your settings and then 'Manage Notifications'. From here you can select the option to get a daily digest email of any mentions (I'd recommend doing this). You also have the option of getting desktop alerts - I personally find them annoying, but if you really want to stay on the ball then they could be a good idea.
The term “organic traffic” is used for referring to the visitors that land on your website as a result of unpaid (“organic”) search results. Organic traffic is the opposite of paid traffic, which defines the visits generated by paid ads. Visitors who are considered organic find your website after using a search engine like Google or Bing, so they are not “referred” by any other website.