The problem used to be that you couldn't listen to a song unless a local radio station was playing it, or you bought it. These days, you can listen to music for free anytime you want.
There is no reason to wait to listen to a song you like, and there's no reason to pay for music. The site and app OnRad.io is a search engine like Google that finds radio stations that are currently playing a song.
For example, the No. 1 song on radio stations is Adele's "Hello." Right now, 20 radio stations are playing it (see photo). Note: OnRad.io scans for songs every few seconds on stations that stream in AAC or MP3.
Just click on one of the stations playing the song, and you can listen to it live. You can also scan through OnRad.io's list of the popular songs. Or, use its search engine to find stations playing songs like the Rolling Stones' "Midnight Rambler."