License Question for new buildup

Hi There!
Im totally new on wordpress. I have bought a book “Wordpress for dummies” and understand, that themes are the optical output of a website.
I´m even not new at the internet. I have a very old website. Its build with WYSIWYG Editor, still build on tables. I want now bring this website to new century.
I dont want to shut down the old page and then rebuild. I want to build the new page with wordpress and then when it runs transfer the page to the old domain.
Im holding actually two domains. One is the running, one is without content.
Can i do with a regular license:

  • Build up the new Page with Theme on Domain B. Make my first steps, try & error in live system
  • After complete transfer the whole project to Domain A and erase it on Domain B.

You don’t understand the working of Wordpress themes very well. Just do your installment where ever you want. In wp-content is a map “themes”. I hope you learned in your dummy book how Wordpress themes are built. In the style.css file in the upper map of the theme between some code is the name of your theme.

You can reach your admin by adding wp-admin to your domain in your browser. You should be able to log in. Go to “Appearance” and then “themes” in your admin to activate your theme. You should recognize the name of your theme you put in style.css so that you activate.

Oh, i´m of course fit with the dashboard and can activate and deactivate themes.
This is no problem.
My probleem is that i build up the new Page with the new theme on Domain B.
After it is finished i want to transfer all to domain A.
If now the bought theme is bound to Domain B it may be not possible. And before i have to buy the theme again i ask here.