DNS stands for Domain Name System. The purpose of DNS is translate your server's IP address into a friendly, easily-legible name that humans can remember. It's much easier for humans to remember a name than it is a string of numbers.
DNS Records direct the different types of traffic for a domain name to the proper server(s). Each DNS Record corresponds to a different type of service or traffic your domain might receive.
A records are set for "hosts" and standard website traffic
CNAME records are set as "Aliases" or Canonical records
MX records direct email traffic
TXT records provide many useful options, like domain ownership verification and enhanced security options
This is not a complete list. You can review all the different DNS Record Types.
Here's a video on how to configure DNS Records: