See where your traffic is coming from by source, from organic search, referrals, paid search etc. then click through to see which leads came from which source.
Social Media sources are sites like Facebook, Twitter, LinkedIn, etc. Websites we can identify as being a social network. For example, someone clicking on a Facebook post linking to your site would be included here.
Referrals are visitors clicked on a link from another site that wasn't classified in any other category. For example, if your site was linked to by a blog and someone clicked the link, it'll show up as a referral.