Once you have a preliminary research question, it is time to investigate the existing data that could be used to address the question. To find existing data, start by searching the published peer-reviewed literature. Google Scholar or an open web search will not necessarily limit your search to peer-reviewed publications and can therefore be a waste of time or cause you to rely on inappropriate work, or both. The easiest way to find peer-reviewed science is to use a database at your institutional library that curates peer-reviewed publications. There are many databases that are useful. Web of Science is one of the most general useful databases, but you can also use databases that are more discipline specific like Georef or BioMed. Ask your librarians for advice to ensure that you are accessing the right papers for your purpose.