How to publish a paper?
First, you should write up your result so it's comprehensible as you can make it, and send it to a journal. If your write-up looks like it is a real research paper, your paper should be sent out for review and possible publication. How to choose a journal? Look for other papers which are on roughly the same subject matter and around the same quality as yours, and see where they got published. 

Don't publish in a fourth-tier journal; if you do, it will never be read; these seem to exist only for the purpose of increasing the number of researcher's publications, and are not subscribed to by many academic libraries. To make sure you're not choosing one of these, check the online databases of a few good academic libraries, and make sure most of them subscribe to the journal you have picked.