Project research is the process of collecting information.
I suggest that you start with fact finding research, which is called secondary research because it is knowledge already discovered by others. These facts are found in books, magazines, software, and from knowledgeable people, such as librarians, teachers, parents, scientists, or other professionals.
While it is not required, if possible exploratory research should be done. Exploratory research is what you discover from hands-on-investigations. What you learn from your own investigations is called primary research.
I do encourage you to collect as much information as possible about the topic you select for your science fair project.
Don’t for get that you need to give credit for information discovered by other researchers. This means that you need to prepare a bibliography listing all the resources you used.
A good way to keep track of the information is to keep a project log–science journal, or whatever you choose to call your collection of information about your science project from start to finish. Information about keeping a project log can be found by clicking this link: Project Log Book.
How you are in developing your project depend largely on how well you understand the topic you choose. The more you read and question people, the broader will be your understanding. As a result, it will be easier for you to explain your projects to other people, especially science fair judges.