Can't listen/play certain songs

[Silverclouds96]

For some reason, I am unable to listen to or even play a few songs that I'd recently downloaded. I'm not sure why, but when I look at my list of songs (whether online or on my desktop app) certain songs appear grey(?).,for lack of a better word, and are unable to be played. 

When I go on to my desktop app, I get a message in blue saying that the song(s) cannot be played, but if I have the file on my computer I can import it. What does that mean exactly? And if needed be, how do I import music on to Spotify??

If it helps, one of the songs I attempted to play was a JPop song called Rain, by BACK-ON.

EDIT: On the Album I downloaded NEW WORLD (by BACK-ON) some of the songs are playable, while other aren't. Again, if it helps at all.