Domain transfers and subdomains

Okay, I just have a couple of questions. I hope I’m putting them in the right place.

Now my first question is domain transfers. I have a domain and a package on dreamhost right now, and I have a domain name on some other site. I was wondering if it was possible to add that domain name to my plan now, but not pay for another plan with dream host. I hope that makes some sense. I think what I’m trying to say is how do I host it with my plan… or something.

My other question is about the subdomains. I don’t know how to get those to work. Like How do I set that up and be able to use it on my FTP program?

Thanks for reading this.