Like most other library resources, Theatre and Drama Premium has a Google-like search box on the home page. Here it is below the banner image, so you may need to scroll down to see it

To search, simply type something in the search box and click on the magnifying glass. To search for a phrase, put quotation marks around the phrase, e.g. "much ado about nothing".  

If you don't use quotation marks, then e.g., for much ado about nothing, you will get results that contain "much" and "ado" and "about" and "nothing". So, chances are you'll end up with more and less relevant results.

That's all there is to basic searching on Theatre and Drama Premium.