Google Web Toolkit for a legacy project

Question

I am working in a legacy web application which means that the project structure is different than an ideal GWT project structure. I would like add GWT for it. I am using intellij as the IDE. Any suggestion or link to any tutorial is highly appreciated.

P.S. I followed this link...but it's is not so helpful. https://www.jetbrains.com/idea/webhelp/adding-a-gwt-facet-to-a-module.html