Help:Introduction to referencing with VisualEditor/5
Verifiability
Why references are important
Adding references
Automatically or manually
Editing existing ones
Always room for improvement
Reusing references
Some are just really useful
Reliable sources
Which sources are good enough?
Summary
Review of what you've learned
Wikipedia articles require reliable, published sources that directly support the information presented in the article. Now you know how to add sources to an article, but which sources should you use?
The word "source" in Wikipedia has three meanings: the work itself (for example, a document, article, paper, or book), the creator of the work (for example, the writer), and the publisher of the work (for example, Cambridge University Press). All three can affect reliability.
Reliable sources are those with a reputation for fact-checking and accuracy. They tend to have an editorial process with multiple people scrutinizing work before it is published.
Whether a source is usable also depends on context. Sources that are reliable for some material are not reliable for other material. For instance, otherwise unreliable self-published sources
These are general guidelines, but the topic of reliable sources is a complicated one, and is impossible to fully cover here. You can find more information at Wikipedia:Verifiability and at Wikipedia:Reliable sources. There is also a list of commonly used sources with information on their reliability.