After adding a domain into your DNS Made Easy account, you can add the necessary subdomains to it.
Subdomain points to an IP
Let's say that our domain subdomain.testserver12.com points to 1.2.3.4. In that case, we would create an A record within the domain testserver12.com of name "user" and the IP value 1.2.3.4 just like in the picture below.
Subdomain points to an FQDN
Our domain user.testserver12.com points to alldomains.com. In that case, we would create a CNAME record of name "user" and "alias to" value "alldomains.com".
Note: if the value does not end in a dot, your domain name will be appended to the value.
In case you have other remaining records types that need to be added within your domain, all you have to keep in mind is that, if you are adding a record for a subdomain, then you would just add the subdomain into the "name" field, and consequently the value.