There are no clear-cut, absolute answers on whether a source is a "good" source, or how to determine one. But there are a few questions that can help you explore whether a source is credible enough to use in a research assignment:
Navigate away from the site itself, and see what other sources have to say about the website or organization. Even taking a look at the Wikipedia page can help!
The first few search results aren't always the best or most helpful sources to use, so take some time to scroll through your results--even looking at the second page!--before you pick a few to click on.
Crash Course's series Navigating Digital Information has a number of great videos explaining different aspects of evaluating information.