DNS is used for directing requests for the domain name, so that the end machine knows how to handle requests. When you access a website a request is sent to the DNS server to direct you to the appropriate web server.
DNS Records are the mapping system for your domain name. Listed below are what each record are used for.
A - The A in A Record stands for address and is the most commonly changed DNS record. This has an IP address responding to the request notifiying it where the server for the domain name is. A Record is used for 32-bit IPv4 addresses.
AAAA - AAAA has the same function as the A Record however it is used for 128-bit Ipv6 address.
CNAME - Canonical name allows one domain to be an alias for another. For example www.test.com could display www.test.co.uk.
MX - MX stands for mail exchange. This record is used for pointing emails to the correct mail server.
PTR - This is the pointer record. This is used for the reverse DNS lookups.
NS - This is the name server record and shows which DNS server is responsible for the DNS for that domain name. There is usually more than one of these records.