Custom Tumblr domain

[MrWhite]

So i want to use a custom Tumblr domain for my blog.
They explain here how to do this, http://www.tumblr.com/docs/en/custom_domains

But i dont understand how to do this in the DNS setting (i have enabled them).
So i have a subdomain like sub.realdomain.com, for that subdomain i want to set it up.

Any1 know how to do this ?

thx

 

[zEitEr]

How does it relate with directadmin cp or its usage? Wrong forum, man.