The link must be the exact title of an existing Wikipedia page, otherwise it will show a
red link. For example, we have an article titled "Kickboxing" so if I put [[Kickboxing]] it will work:
Kickboxing. We do not have an article called "Kick-boxer", so [[Kick-boxer]] will result in a red link,
Kick-boxer.
If you wanted to link the word "Kick-boxer" to the article on Kickboxing, this can be done with [[Kickboxing|Kick-boxer]] which links the word "Kick-boxer" to the article "Kickboxing", and appears like this:
Kick-boxer.