Project Navigator in Xcode with folders and files has nothing to do with the files in the project folder in Finder. You will see that the navigator contains “folders” that do not even exist in the directory on the Mac.
Once you drop the files into the project directory, you need to add them to the project. Right-click the folder in the navigator where you would like to include files, and select "add files to your project name"
Alternatively, you can drag and drop files from one Xcode project to another in the navigator.
Hope this helps.