Help:Introduction to referencing with VisualEditor/1
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

One of the key policies of Wikipedia is that all article content has to be verifiable. This means that a reliable source must be able to support the material. All quotations and any material whose verifiability has been challenged or is likely to be challenged must include an inline citation of a source that directly supports the material. This also means that this is no place for original work, archival findings that have not been published, or evidence from any source that has not been published.
If you are adding such new content, it is your responsibility to add source information along with it. Material provided without a source may be removed from an article. Sometimes such material will be tagged first with the {{citation needed}}
template to give editors time to find and add sources.
This tutorial will show you how to add inline citations to your articles, and also briefly explain what counts as a reliable source.