After having explored and defined your subject, your subject can be translated into a specific and clearly defined problem definition.
A solid problem definition usually answers the questions who?, what, where? and when?
Let's assume you have to write a paper on the role energy plays in animal behavior. Based on the exploratory phase and a few simple questions, you could easily come to a clearly defined problem definition:
What? The energy costs of courtship display in birds
When? During breeding or courtship season
What is the objective of the paper? Query behavioral ecology
Problem definition: what are the costs of courtship display in birds during breeding season in terms of their energy management?
For your info: in view of the specific problem definition, following questions are also important to get a clear view on your assignment.
How much time did you get for the assignment? For looking up references and reading documents takes some time and you need to plan realistically.
How extensive does your paper need to be? In some cases you may limit yourself to recent literature; in others you are required to set up an exhaustive reference list and, as such, work with older literature as well.
What is the exact assignment? In some cases you may limit yourself to collecting the literary works, in others you must compare them critically with each other as well.