We write to explain what we have done, how we have done it, what we found, and why it matters.  (Alternatively, you can rephrase all these things in a future tense when you are proposing to do research.) 

Technical writing has to involve a logical structure from problem to solution to evaluation.  But before you are at the stage of writing down all the details, it is often a useful exercise to write down just that logical structure.  Then, your mentor can see whether the ideas hold together.