There are several types of content that can be added to the wiki such as Videos, or Images. A quick guide to that is found here: Adding Content Samples
Editing most Wikipedia pages is easy. Simply click on the "edit" tab at the top of a Wikipedia page (or on a section-edit link). This will bring you to a new page with a text box containing the editable text of the current page.
In this box, you can type in the text that you want to add, using wiki markup to format the text and add other elements like images and tables. A quick reference to wiki markup can be opened in a new window by clicking 'Editing help', found near the 'save page' button.
Never start a line with a leading space unless you want the special formatting it causes. Paragraphs can be separated with a blank line.
When you have finished editing, you should write a short edit summary in the small field below the edit-box. You may use shorthand to describe your changes, as described in the legend. To see how the page looks with your edits, press the "Show preview" button. To see the differences between the page with your edits and the previous version of the page, press the "Show changes" button. If you're satisfied with what you see, be bold and press the "Save page" button. Your changes will immediately be visible to all Wikipedia users.
Note: Do not sign the Edit Summary line with your ~~~~ signature as it does not work here.
The Wikipedia community has developed style guidelines to make articles and facts appear in a standardized form, and Wikipedia easier to use as a whole.
Help:Wiki markup is the extra information (apart from the text which will be displayed) you enter in the edit window which tells the MediaWiki software how to display, categorize and process the article.