The most reliable way to find peer review articles is using a library database. Library databases are made up almost entirely of scholarly sources and do not include any paid content like you find on the web. Below is a list of the library databases that would be most useful for this project. The interface of each database may look a little different, but the functionality will be very similar. Start with very simple search terms. You can always add more, or be more specific as you go. Avoid typing in phrases like you would in google. For example, in google you might type, "What are the harmful effects of secondhand smoke?" In a library database you would type, secondhand smoke AND harmful effects.
If you're having a hard time getting relevant search results, you may want to try the chat feature on the library website for help. A librarian is available 8am - midnight during the week to answer these questions. Alternatively, send me an email and I can help you come up with a search strategy, email@example.com