What is a UTM tag?
It is a short label added to the end of a web address. Analytics tools such as Google Analytics read it and report where the visit came from, so you can tell a Facebook post from an email.
What should I put in source, medium and campaign?
Source is where the link lives, such as facebook or newsletter. Medium is the type, such as social, email or cpc. Campaign is the name of the push, such as spring-offer. Keep the names short and use the same ones every time.
Does this change how the page looks?
No. Visitors see the same page. The tags only travel in the address, so they are best kept for links you share, not for links inside your own site.
Is anything sent to Binfield?
No. The link is built in your browser and nothing is stored.