For each user who comes to your site the google analytics automatically capture the traffic source dimensions Source, Medium, Campaign name.
Step-by-step explanation:
Source:
- There cannot be any reference to a website without an origin source.
- The source is basically the origin of your traffic such as a search engine (google) or a domain (ex: Twitter).
Medium:
- Every referral to a website also has a medium along with the source.
- examples are -: unpaid search, "cost per click", referral, mail.
Campaign name:
- The campaign Name is the name referring to the google ads campaign.