This is an exciting process, but it can be frustrating. The first thing to do is get passionate about something -- some aspect of your field. You should read lots of articles -- recent articles -- and you will see that they all give background information and explain the progress that has been made and what kinds of research projects are missing from the literature.
For example, I am interested in the bioelectricity that is manipulated in Chinese medicine. Therefore, I know what new research needs to be done in the field. I know that we should experiment with electrical stimulation as a form of therapy -- and this is already being done -- but my knowledge of what is going on in the field enables me to know what a good topic is.
When you choose your topic, give the synopsis in a succinct way -- not extra phrases or sentences. Look at 10 different articles online and read the "abstract." That will show you what to do. en.wikipedia.org/wiki/Abstract_%28summary%29
What you are writing is not exactly an abstract, but this will help you. How long is your synopsis supposed to be?