Please read the following in order to understand how Wiki Site works in Sharepoint.  It is very similar to usual way of wiki we are using on http://en.wikipedia.org/wiki/Wiki  If you are new to Wiki's world, it is good that you should read following description to make yourself acquainted of how Wiki works.

Editing wiki pages
This wiki library provides what-you-see-is-what-you-get (WYSIWYG) editing. To edit a page, click Edit at the top of the page. You can insert tables and pictures with the click of a button. When you are happy with your changes you can click OK to update the page.

Creating links to pages
You can link to another page in this wiki library by enclosing the name of the page in double brackets on the edit form. For example, type [[Home]] to create a link to the page named Home and [[How To Use This Wiki Library]] to create a link to this page.

To create a link to a page and have the link display different text than the page name, type a pipe character (|) after the page name, and then type the display text. For example, type [[Home|Home Page]] to create the link labeled Home Page that points to the page named Home.

To display double opening or closing brackets without making a link, type a backslash before the two brackets. For example, \[[ or \]].

Creating pages
There are two main ways to create a new page in your wiki library:

1. Create a forward link to another page and then click on it to create the page:
   This is the recommended way to create a page because it is easier for people to find the page when another page links to it.
   
   Forward links to pages that do not exist have a dashed underline. Start by adding the link (follow the Creating links to pages process earlier on this page). Click the link to go to the Create Page form where you can start typing your content.
   
   
2. Create a page that is not linked to any other:
   In the Recent Changes section, click View All Pages. Then, on the New menu, click New Wiki Page. This takes you to the Create Page form where you can start typing your content.

Managing your wiki library
You can manage the pages in your wiki library by clicking View All Pages in the Recent Changes section.

Restoring a page
If you need to restore a previous version of a page, click History at the top of the page. You can then click on any of the dates to view the page as it existed on that date. When you find the version that you want to restore, click Restore this version on the toolbar.

Viewing incoming links
You can see which pages link to the current page by clicking Incoming Links at the top of the page.

Now, as you have read the description, lets begin with implementation of that one-by-one.

To Edit Page click on Edit Link from Top-Right corner of Wiki site.

On click Edit Link you are been taken to Edit Page of Wiki Site.  As you can see in figure, you will see WYSIWG Editor to Edit Wiki Page.

Ones you are done editing you should click on "OK" button to apply the changes.

After you are done with Editing Page, Page can be viewed as follow by every visitors of this page.

To create External Link on Wiki Page, open the wiki page in Edit Mode by clicking edit link from Top-Right corner.  On Edit Page select the text you on which you would like to open external link and click link button. 

 In Insert Hyperlink dialog box enter the Url you wish to link.

And to create Internal Link, that is link to any of sharepoint page.  Let say i would wish to create link to Home Page than you can create link to that page by simply writing page name in double square bracket.  [[Home|Home Page]]

Page looks as below after you have created link.