Help:Introduction to referencing

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

If you are adding new content, it is your responsibility to add source information along with it. Material provided without a source is more likely to be removed from an article. Sometimes such material will be tagged first with a template to give editors time to find and add sources before it is removed, but sometimes editors will simply remove it because they question its veracity.

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Wikipedia