That specific song you say, I'm taking a guess that you are talking about local files. If you are talking about local files (which can't be found in the search engine in Spotify but you have to import it yourself), you either:
A: Go to Youtube, find your song, copy the URL, go to Youtube to MP3 converter and download the song.
B: Buy your song in iTunes.
If you don't have a Mac but you have Windows, download iTunes in your Windows and do the steps. You need a computer to make this work.
OH you touch my tra la la...Mmm, my ding ding dong. So rock your body! Come on, come on! Rock your body! Now move your hips and dance like fish! My style is di bom digi bom di deng di deng digigi