Creating new designs for emails

Hi:

I am new to Marketo and am starting to get a good grasp on things. I have the email templated that were prepared for me by the Marketo Team, but I may be interested in using some additioal designs ot to changing the designs of the existing templates. Can anyone supply some information on the best and easiest way to do that? Can I just copy HTML from another email template program into the email when I edit it? Or, is there any other way to do this?  ANy tips would be helpful.

Thank you.

Paul