Res Folder

Hello I have really just started Coding in Java a few weeks ago and I thought my first project would be an MP3Player. Then code more and more to get a better grasp. One question I would like to ask is how do I like setup my res folder in my project, then load pics from it for my JFrame’s background or a buttons background? Thanks for any help guys. I have my JFrame’s background set and my custom buttons but I can’t jar it for friends to test until I get this problem fixed.