A records are the basis of the zone. They are used to assign an IP address to correspond with a web host. The purpose of this is to define where the host will be "redirected", such as setting the your-domain.com host to point to the IP of the web server where the files are stored. They are also used in conjunction with MX records to set up a host, mail.your-domain.com, that points to the IP address of the mail server that will be accepting e-mail relative to this domain.
