In From First Draft to Finished Novel, Karen Wiesner talks about after brainstorming comes Research. Her take on research is more extensive than my take but more on that later.
During this phase of the story the first thing is to discover the areas where you'll need to do Research before beginning. The place you've chosen, the occupations of the main characters, the era you've chosen. Anything that needs to be discovered about person, place or thing. Once you've discovered all the things you'll need to discover while writing the book, you can Collect the material you need. For me, this often means books or on-line sites marked to return to again and again. Those are written down, though I do love books to leaf through and force myself not to start reading and reading. Reading is the next step in the process Karen speaks of. This is not a good time for many writer since one interesting fact leads to another. From here you go to Using. How and where in the story you're planning to write will you use this material? You may also find doing this research ideas for other stories. That's a good plus.
For me, I begin my stories by fitting a set of characters to plot and the plot to the characters. Then I decide what I might need to know and do my research after the story is roughed on paper. There are notes throughout my first drafts that say things like. Look up. Talk to. Find what can be used. But I always know before I begin what the story features, where the story takes place.