Here is a link to a very good article that explains rights.
http://www.writing-world.com/rights/rights.shtml
It is important to know what rights you are selling--IF you are selling. I.e. if you are getting money for it.
If you are just letting someone publish it without getting anything besides a copy or two or the journals, there is usually a statement that all rights revert to you with a certain time and all the editor asks is that you mention the first place of publication if you republish it in a book or in some other magazine or online.
In North America, if you are accepted by a paying journal you will usually be asked to affirm that they are buying the First North American Serial Rights. This is an old, old practice and you should take it seriously.
My advice is to not mess around with editors--show them the same respect that you want to shown--that both parties are professional.