Reliable references to reliable sources are what make Wikipedia an authoritative encyclopedia. Therefore, it is critical that good articles be also well-referenced. This tutorial shows you how to add references to your articles. References are also called "citations".
Footnotes are not references, but rather short notes that explain something that would be distracting if it were in the main text. However, they have a similar form to references; once you learn one, the other is easy!
Both references and footnotes are numbered automatically; you don't have to worry about assigning numbers to them. Both can be labeled with a name tag for easy re-use, as described below.
How to add references
editTo create a new reference, you need to enclose the citation between two tags, the "opening" tag <ref> and the "closing" tag </ref>. (The difference lies in the forward slash in the "closing" tag. For illustration, if you write
Horses have a skeleton that averages 205 bones.<ref name=Evans90>Evans, ''The Horse'' p. 90.</ref>
that will produce
- Horses have a skeleton that averages 205 bones.[1]
For speed, you can highlight the reference text in the editing window, and then click on the 
button in the editing toolbar. That will enclose the text in ref tags.
You should note two Wikipedian customs from the example above. First, the reference tag goes after the punctuation mark, which is a period in this case. This practice differs from many scholarly journals. Second, you can add a name to each new reference, which you can use to cite the reference elsewhere in the article. To do that, use only an "opening" tag but end it with /> rather than >. For example, if you write
The femur of a horse is unusually long.<ref name=Evans90 />
that will produce
- The femur of a horse is unusually long.[1]
To see the references, you should first add a section with the heading "References". This section is always after the "See also" and "Footnote" sections (if any) and before the "Bibliography", "Further reading" and "External links" sections. Into the new References section, add the tag <references />; please notice that the tag ends with /> rather than >. This should produce something like the "References" section near the bottom of this tutorial. You may click on the [edit] link in the References section to see the tag in context.
Note that the superscripted numbers of the two citations above are the same, reflecting the fact that they point to the same reference. If you click on either number, you'll be taken to the corresponding reference below. At the beginning of that reference, you'll see two superscript letters a and b. These correspond to the two citations of that reference in the main article. Clicking on either of them will return you to the place in the text where the reference was cited.
When you're first learning to use references, it's simplest to write out the reference by hand. As shown in an earlier tutorial, italics and boldface type are made by enclosing the text in two or three single quotes, respectively. As you get more practice with references, you can also use citation templates, which allow for more consistency in reference format across Wikipedia. These templates will be covered in a later tutorial.
How to add footnotes
editReferences and footnotes serve different purposes, as explained above. References are citations to reliable sources that support the assertions in the article. Footnotes are short explanatory notes that would be distracting if they were incorporated into the main article.
However, references and footnotes on Wikipedia are produced in a very similar way. The chief difference is that a "group=" parameter is added to both the <ref> and <references> tags. The value of the group parameter is what appears in the footnote itself.
For illustration, consider the following command
Sphinx of black quartz, judge my vow.<ref group="note" name="pangram">This sentence is a [[pangram]], a sentence in which every letter of the alphabet appears.</ref>
which produces the following:
- Sphinx of black quartz, judge my vow.[note 1]
To see the footnotes, you should first add a section with the heading "Footnotes". This section is usually after the "See also" section but before the "References" section. Into the new Footnotes section, add the tag <references group="note" />; please notice that the tag ends with /> rather than >. This should produce something like the "Footnotes" section below. You may click on the [edit] link in the Footnotes section to see the tag in context.
Authors can decide on their own group name, and even have multiple groups. However, such complications are discouraged, especially if casual readers might be confused by them!