You can also add a citation using Wikicode.

You can access Wikicode from edit mode by clicking the pencil icon and selecting "Source editing".

Then, follow these instructions:

1. Check that the bottom of the page has a "References" or "Notes" section. If not, type: ==References==.
2. Check that the References section either has the text {{reflist}} or <references />. If not, type: {{reflist}}. This determines where your references will appear on the page.
3. Now click after the text you would like to create a reference for.
4. Now type in the <ref> tag before your reference and type </ref> after your reference. Wikipedia's software will automatically add your inline reference number.