For an overview of a topic, I typically go to a database of encyclopedia-type references such as Credo Reference or Science in Context. On these particular databases you can find short articles from sources like the Environmental Encyclopedia, The Gale Encyclopedia of Science, etc, that are credible but much more approachable than the typical journal article.
Once I get a genral understanding from sources like that, I go to Science Direct, ACS Journals, SciFinder, or others, to get detailed info and references for my papers or presentations.
I suggest going to your school library reference desk and explain to them what you're after. Your school may have a subscription to the two I mentioned above (which is required, unfortunately), or to similar databases.
Good luck.