Question: Kindle for PC app?
Once you've successfully installed Kindle for PC on your computer, if you open the .Mobi file that you downloaded (make sure it is the .mobi version as that is the only one that will work with Kindle for PC!), if you then try to open the .Mobi file, it should automatically open in Kindle for PC. If not, try to right click on the .Mobi, and select the option to "Open With" and choose Kindle for PC. Enjoy the book!