Wiki has several ways for constructing links. Mainly they all derivate from the initial form:

[[the_link]] or
[[the_link][the_text_to_show]] or
[[the_link][img the_image]]

[[http://www.turro.org]]

[[http://www.turro.org][turro.org]]

[[http://www.turro.org][img repository(/powered.png)]]

Links with new target

You can create links that point to external sources or will create new a tab on the browser and make it clear to the visitor with ext or new:

[new[http://www.turro.org][turro.org]]

[ext[http://www.turro.org][img repository(/powered.png)]]

Links with markup

Modern responsive frameworks require class assignments to links. In that case, you can use links with markup. The URL reference must be the first markup parameter.

Wiki	Result
[link(http://www.turro.org)] turro.org [/link]	turro.org
[link(http://www.turro.org)] [img repository(/powered.png)] [/link]
[link(http://www.turro.org,&class:ui primary button)] turro.org [/link]	turro.org

The last example take advantage from Semantic-ui, used in this site.