Help:Introduction to referencing with Wiki Markup/3
Verifiability
Why references are important
Inline citations
How to add them
RefToolbar
Citations the easy way
Reliable sources
Which sources are good enough?
Summary
Review of what you've learned
Manually adding references can be a slow and tricky process. Fortunately, there is a tool called "RefToolbar" built into the Wikipedia edit window, which makes it much easier.
To activate it, simply click on 
Cite at the top of the edit window. Position the edit window cursor after the fact or sentence you wish to reference, and then select one of the templates from the dropdown menu. There are different templates suitable for different types of sources:
{{cite web}}for references to general websites{{cite news}}for newspapers and news websites{{cite book}}for references to books{{cite journal}}for magazines, academic journals, and papers
This will pop up a window, where you fill in as much information as possible about the source, and give a unique name for it in the "Name" field. Click the "Insert" button, which will add the required wikitext in the edit window.
Some fields (such as a web address, also known as a URL) will have a 
icon next to them. After filling in this field, you can click it to handily autofill the remaining fields. It doesn't always work properly, though, so be sure to be sure to double check it.
Often, you will want to use the same source more than once in an article to support multiple facts. In this case, you can click Named references 
in the toolbar, and select a previously added source to re-use.
Please note, the RefToolbar is not available unless it is turned on via a user's Prefernces page. It is on the "Gadgets": tab in the "Editing" section of that tab.