Editing a Wiki page is very easy. Simply click on the "edit" tab at the top (or the edit link on the right or bottom) of a Wiki page. This will bring you to a page with a text box containing the editable text of that page. If you just want to experiment, please do so in the Sandbox
Creating a page
To create a new page, do a search with the exact title of the page you wish to create. Try to keep the new page names relatively short if possible. If the page does not already exist you will see:
Create the page "<pagename>" on this wiki!
Click the link and you will be taken to a new page with the title you just searched for, add any content you want and there you go, you have created a new page!
Editing a page