If you mean a story (fiction) that you have written, and if you mean by "for free" that you don't get paid for it, there are websites where amateur writers can post their work. You can search for them using Google.
If you mean how can you get your story into a magazine, thousands of writers are busy trying to do that every day. Do your research and take your best shot.
If you mean by "for free" that you don't have to pay, that standard is fading away. Many legitimate publications now charge reading fees. It used to be true that no real publisher would ask you for money before they would read your story, but that standard has gone away. Traditional publishing has taken a huge hit from the Internet and from rising printing and mailing costs, and this is one way that it shows.