1) Login to your cpanel account e.g. http://yourdomain.com/cpanel. Under Domains section, click on Zone Editor.
Zone Editor allow user to create and delete A, CNAME and MX records in a domain's zone file.
2) Click on either A Record, CNAME or MX Record to enter your desired details.
3) If you are adding an A record, do as shown by the example below.
For example, mail.domain.com IN A 220.127.116.11
If you are adding CNAME record, do as shown by the example below.
For example, mail.domain.com IN CNAME domain2.com.