Can you describe what happens when you run the installer for DPP?

As for connecting a camera or card reader (or using the internal SD slot), in Finder select Finder menu > Settings and on the General and/or Sidebar tabs, tick the box to show External disks. Then any connected memory card will show up on the desktop and/or sidebar (in a Finder window, locations section). You can just double click it, open the right one of the two folders and your images can be dragged where you want them.