(Please note that the 500 words is an upper limit and not a target; you may well be able to make a good job of this in rather less).
Aims: What will your session try to do? Bullet points work well here - these should reflect your intended audience as well. Be realistic about what is possible in a 55 minute session.
Background: Provide a brief description of why you have taken an interest in this aspect and how you have developed it. It might be from your own classroom or prep room practice, from working with colleagues, reading or seeing some piece of work or a collaborative research project. Avoid unnecessary detail but give the committee an outline 'back story'.
Synopsis: This can be usefully written as 'participant facing' material; describe to people who might be considering attending your session what it will be about and what they will gain from it.
Outcomes: These are best framed as behaviours - what will participants be able to do as a result of attending the session. Again, be realistic about what can be achieved in the available time but be clear as well.
(Please note the 300 words is an upper limit not a target).
Conference sessions should be based on more than a hunch or vague assumptions about what supports effective education. The evidence base could come from a range of different sources, such as classroom observations, data analysis, published materials, research projects, etc. Be prepared to cast the net wide but do indicate what supports the ideas in your session.