Once you Right click on Properties, Customize will be one of the tabs at the top. Click on it and then go to Choose File. This will take you to a Browse option where you can choose the file folder with your Image you are wanting. Choose the file and Open, then Apply & Save, and your Image will automatically be there.
Hope this isn't as clear as mud, lol.
Good luck, and btw...NO question is a stupid question when you are learning. We all were new at one time, and most of us, me included, are still learning!