When you create a new Publisher project, you specify the project's name, source files, and initial style mapping using the New Project Wizard. Once Publisher has created the project, the last screen of the wizard gives you the option of converting your source files right away or saving the process until later.
To generate the content, select the Yes, go head and convert the content now radio button; to covert the project later, select the No, I'll convert the content later radio button. If your project is large or complex, you may want to convert the project later since the conversion process may take several minutes.