A page is created in a wiki by making a link to it. To avoid creating a link to an existing page please name the page initially by the section under which it was created. i.e. onthe main page, the page "oil change" wasn't created on its own as this may collide with oil change information from different engines, so I have created the page "petrol engines oil change" to avoid a clash. If in doubt create a long descriptive name to avoid duplicate links, but use a shortened link to display. The bit after the two square brakets on the left (you'll see the formating when you click the edit tab above) is the name of the link to the page page, AND the name of the page that is created. The bit after the 'pipe' or the vertical line (shift+backslash) is the text that is actually shown rather than the long descriptive page name that you created, this will help to keep the layout on this initial page as tidy as possible.
See Also Descriptive links