Once the research is complete, a research proposal helps in evaluating whether the objectives were met.
A research proposal is a statement of how you intend to carry out your research.
It is essentially stating what you are going to investigate and how you plan to accomplish your investigation.
There are no boundaries when it comes to determining what you want to research; you can literally research anything.
Research is getting out there and measuring, collecting samples, reading, and interpreting data or texts. When you are ready to write a research proposal, you should already have an idea of what you would like to investigate, but you are not investigating anything just yet.
For example: What are the migration behaviors of Mallard ducks?