Now, this may be a euphemism for "this is crap but nice try," or it could actually be a comment to take at face value. I got a rejection for a journal for one of my stories which said: "this is a nice story, would have been great with the issue of our previous theme but not for the next one," which is actually a nice rejection, you'll notice that a lot of writers are happy with nice rejections, a fact most non-writers may fail to understand.
When beginning the long and painful process of trying to publish your short stories, you decide to play a lottery of submitting things to as many journals as possible and hope that the law of probabilities means that someone will eventually pick your work. How many of us read the submissions and conveniently ignore the bit that says "please buy our journal and see what we're about and if you're right for us" when we're just desperate to get published? I've purchased a few journals, but I have been too
I got lucky with my story which was published in the Writers Abroad anthology - it was a perfect fit to the theme they were looking for. Since then I've had the brainwave to start searching for anthologies and submission calls which fit the stories I already have to offer. While you need to still have a strong piece to submit and while not any old crap will do, actually submitting to something which fits the criteria for the anthology/journal opens up the probabilities a lot! This really should be common sense, but it's also a lot harder work for the budding writer - there are so many journals and anthologies out there, how to find them?
Duotrope's Digest is a fantastic resource for looking for the right journal or anthology for you. It has EVERYTHING listed on here. Just look up anthologies only and already you're faced with a bunch of themed anthologies to pick from currently calling for submissions - maybe there is something there perfect for you? Or even something which looks interesting to write for, just for fun and to try your luck
You can also sign up to various journal's mailing list and get updates and submission calls for their themes their interested in. With a little work the opportunities will start to come, and once you start submitting your work which a magazine, anthology, or journal is looking for you might find you're more likely to find an acceptance letter than a rejection.