Most of these resources link to reference sources of some sort.
Reference Sources summarize a topic. They tell you basic things, like when and where an event happened, a simple or introductory description of an idea or theory, or the most important points about a person's life.
Reference sources generally do not offer analysis, and if writing about a controversial issue, will usually remain neutral.
Reference sources are useful for choosing a topic to write about, and for learning enough about a topic to allow you to find and understand more detailed sources like books or journal articles. They can lead you to more detailed or interesting sources.
Because they summarize the information found in other sources, add no new analysis or ideas, and intentionally avoid going into too much detail or making an argument, however, they are not good sources to cite in a research paper.
Wikipedia is an unusual encyclopedia. It averages out to be about as accurate as more traditional paper encyclopedias, but there are a few reasons that you should approach it skeptically.
Wikipedia's average quality is good, but some articles are much better than others. Some Wikipedia articles are well researched, unbiased, and clearly written. Some Wikipedia articles are incomplete, full of authorial bias, lack citations or references, include the author's opinion as fact, use unclear or grammatically incorrect language, and are a mess. Most wikipedia articles are somewhere between those extremes, but the uneven quality is one reason to be careful about relying too much on Wikipedia.
Wikipedia is a group project, and everyone that edits it does so anonymously or using a screen name. It is hard to verify that the people who have written or worked on an article are knowledgeable about their topic, and an article is often the product of many people's writing and editing.
Wikipedia articles often change. Unless an article has been locked, Wikipedia articles are always subject to change. Often the change is improvement, but not always. Wikipedia is a "living" document in the sense that articles are never "finished", but are instead constantly changing, being edited or rewritten, and so on. Large, high quality articles are less likely to change dramatically than smaller articles in need of improvement.
