Your question is vague. I'm going to assume you know how to layout the book in Indesign. So, to export the PDF you go to File - Export - then for Format you choose PDF and give the file the name that you want it to have and browse to where you want the file to go. Then you click OK and you can set up all of the options for the PDF that you're exporting. Submit a more detailed question for a more specific response.