The name of a page has a special syntax known as a WikiWord. A WikiWord starts with a capital letter and has at least one more capital letter in it. Between the capitals there must be lower case letters or numbers. There cannot be two capitals in a row.
If you place a WikiWord in the markup text, but no such page exists, then you will see something like this on the page:
If you click on the question mark it will create that page for you, and allow you to edit it.
If the link to other pages is long, such as the link to a page in another SubWiki like <User Guide .Fit Nesse Wiki .Sub Wiki, then the link can replaced with easier to read text by using this markup:
[[text shown on screen][<LinkToOther.SubWiki]]