First login to DirectAdmin. Once logged in, navigate to the Account Manager --> DNS Management section of DirectAdmin as noted below, and click the DNS Management link: 
Once the new page has loaded, this next page will have a list of the DNS records on your account, and options to add an A, CNAME, or MX record, and the Manage link will allow you to edit or remove existing records, or add advanced types of DNS records.
To add a record, click the Add Record button. This will bring up a popup window, with a dropdown menu, to enter the record information.
Adding an "A" Record
Choose the appropriate type of DNS record to add/edit.
For an 'A' record, type in the address of the A record in the Name box, ending with a period. For example, a subdomain could be "subdomain.example.com." Then enter the IP address it should point to in the Address field, and click the Add button.
(Don't forget to include the "." at the end, or you will see a warning as shown in the image below.)
Adding a CNAME Record
To add a CNAME record, click the Add Record button and choose CNAME from the dropdown menu. Fill in the prefixed domain, followed by a period, in the Name box. For a CNAME record, the Address will be a domain it should point to instead of an IP Address.
Adding an MX (email) Record
For an MX record, the first box will be Priority. This will be a number indicating which record should be tried first, with lower numbers being higher priority. For example, the first record it should try can be Priority 0, and then if you add another MX record as Priority 5, and another as Priority 10, it will try the 0 record first, then if that fails it will fall back and try the 5 record, then the 10 record. The destination will be the domain or subdomain it should point to, ending with a period like "mail.example.com." If you are trying to update the MX record for an "alias" domain, you may need to just delete the old record and add a new one.
