If you own a new computer (i.e. one purchased after the turn of the Millennium) you'll more than likely have an MP3 player on your computer. The easiest way to find out if your computer is furnished with one is to download an MP3 file from the Internet and double click it.
If you have a suitable player installed, the MP3 will play, if not you will need to download and install one. There are dozens, if not hundreds, of MP3 players are available to download on the Internet.
Here are some of the most popular: