Writing is an art and if you are good in that there are a number of sites where you can submit your work. There are some sites pertaining to popular magazines but they publish only 1 or 2 fictions per month as other general materials are there in them so the competition for publishing is much there. Another option could be to make a blog in some blog site and start writing and once the quality of stories is good slowly traffic would increase. If you have objective of improving your English language writing and later transform it to story writing then you can contribute in ISC also as many people have benefited here and improved their writing skills. This is basically an educational site and if you have only one interest of publishing fiction then that would not be encouraged here much but yes learning the writing part that can be accomplished here.
There are many good sites in internet where fiction can be uploaded and some of them are -Commaful, Wattpad, Smashwords, Archive of our Own, Fanfiction, Figment (RIP), Medium, FictionPress, Smashwords, Quotev, Tumblr, WritersCafe, Booksie, RoyalRoad, Hubpages, The Young Writers Society, FanStory etc.
Please note that they have their own terms and conditions and you have to go through them before submitting your product. Some of them pay you also for your work while some share revenue under some schemes.
Knowledge is power.