It depends. You may be after an evidence-based article. You may need a quick fact. In either case, what you're really after is authoritative information, which can take many different forms. At its most basic level, this is any information created by someone who is an authority on that subject (typically a researcher or expert in that field).
For any information you find, ask yourself some of these questions:
It can be easy to slip into the mode of accepting information at face value. Do your best to overcome this! Try to get in the habit of fact-checking things, even if they seem like they're from an authoritative source (see: American College of Pediatricians vs. American Academy of Pediatrics).
Here are some places to start looking for information related to your class and assignments. The first few are library resources that will help you find mostly peer-reviewed, evidence-based information.
If you're looking for professional organizations, this list from Berea College may be a good starting point.
Most literature indexes do not have the actual journal articles included within them. Instead, these indexes just contain information about the article, e.g. titles, authors, abstract.
When you find an article of interest in an index, click the "Find It" button by that entry to get to the full text. If we have a subscription, "Find It" will provide a link to the journal article. (Or if we have the print, it will provide a link to the catalog with the location and call number.)
(A few databases, like Academic Search Complete, include full text for some articles. These databases may allow you to search only for articles available in full text, but be aware that you are only searching a small portion of the articles we actually subscribe to.)