Everyone has a view on how the world works. You might think that facts are objective. Your housemate might think they are subjectively constructed by individuals. Both of those views are examples of an ontology.
Identifying your ontology is an important part of your research as it informs the rest of your research design.
For example, if you believe in the objective nature of facts you would be likely to adopt an experimental or a quantitative methodology in order to collect hard facts as part of your research design. You would be unlikely to adopt a qualitative methodology that explores the nature of facts.
There is a range of ontologies including realism (which adopts an objectivist view), actualism, metaphysics, and constructivism (subjectivist). You should explore them all briefly and work out what you think best reflects your attitude and understanding of the world before continuing with your project.