Go to your Home folder. You have to make hidden files/folders visible, so hit Ctrl+H. Go to the directory named .gimp-2.x (where 2.x is version number of GIMP you are using).Within that folder, there are subfolders, one of which is plugins. Drop your plugin into that folder.
Ik weet nu ook hoe ik nautilus moet openen voor de toekomst.