I'm trying to download some songs onto my iPhone (5S, iOS 7), but they are just grey with this little broken circle next to them. Can anyone explain what's going on? I have space on my phone, and when I don't, my computer tells me, but here the songs are just kind of there. Please help!

I'm trying to download some songs onto my iPhone (5S, iOS 7), but they are just grey with this little broken circle next to them. Can anyone explain what's going on? I have space on my phone, and when I don't, my computer tells me, but here the songs are just kind of there.