I use 123-reg as my domain registrar, I found this DNS Management Guide on there site.

Its not a very big book; but it gives a nice quick overview to DNS, and gives examples of how to use different records.

A records, CNAME records, MX records, nameservers…… confused?

What will this guide help me with?

This guide contains information on the following areas:

• What is DNS?
• What are subdomains?
• What are nameservers?
• How do I check my nameservers?
• How do I change my nameservers?
• Setting up an A record
• Setting up a CNAME record
• Setting up a TXT record
• Setting up an SPF record
• Setting up an MX record
• How do I point to my own mail server?