I'd also suggest you go straight to www.amazon.com and look for "Pricing Photography" by Michal Heron. This book helps you arrive at an asking price, explains how to negotiate, the shows you sample forms you can use as contracts, and neatly explains the terminology that's used in those forms.
Heron now has a companion book :"Stock Photography Business Forms: Everything You Need to Succeed in Stock Photography". I haven't got it yet, but it looks useful. He's written several others about stock photography, too.
There are a lot of questions you need to ask the publisher, to arrive at an initial, fair asking price (see "Pricing Photography" for guidelines to both).
Then the negotiations can begin.
It doesn't hurt to first ask what they offer, though. In the case of a magazine, they may have a set "pay rate" (but usually have some latitude for exceptional images, so don't let them tell you it's set in stone).
There's also "Business and Legal Forms for Photographers", written by Tad Crawford and co-published by ASMP. Among other things, it includes image licensing forms and lots of explanations about them.
The difference is that you are licensing limited usage of your image... It might help to think of it as renting it out for a set period of time, allowing only so many copies of it to be printed and having some limitations on the distribution of those copies. All these things are negotiated and then spelled out in detail in the image license.
Selling, on the other hand, means or at least implies a complete transfer of ownership, which is something you'd want to carefully avoid if you have any prospects to make additional income off the image in the future.
Nice photo, by the way.