The field of Public Health by its nature is very interdisciplinary. Much literature can be found in PubMed - see how to find search terms and conduct a comprehensive search in PubMed in the videos towards the bottom of this webpage.
Depending on your topic you may need to search elsewhere, such as the DiscoverUR on the library website, Google Scholar, or other disciplinary databases such as PsycINFO.
If you're focusing on health interventions and other public health programming you will probably want to search for grey literature online.
You can also get a good overview of the topic for your literature review by reading through systematic reviews, which can be found in the TRIP database.