Software :: Can't Put Music Files In Music Folder

I have some sound effects that I have on my external hard drive that I want to listen to and add to my iTunes, but whenever I go to do that I get a message that says I don't have permission to write on my music folder. I am the only account on my Macbook Pro. I checked and I have the rights to read and write on my music folder. I don't know how to fix the problem. It also happens when I add music that I downloaded from the internet not iTunes. Sometimes with that I just have to hold option or command (I don't remember off the top of my head) and that'll let me copy the music into a folder that I created. How can I get permission to write into/onto my music folder for my Macbook Pro?