External links are links to pages in another website, or also in the local server. You can also use this method for internal links, but normally that is done with the double square brackets [[]].
Let's say URL is the full url of a file or page on another website. And Name is the name of the site, or the page.
You write:
[URL Name]
What will be shown is only 'Name' as a blue link.
For example:
[https://en.wikipedia.org/wiki/Korea_under_Japanese_rule Wikipedia: Korea under Japanese rule]
shows up like this:
Wikipedia: Korea under Japanese rule
You want to make sure to write a text for the blue link that is made. You can also leave this out and then you get this:
[http://mediawiki.org]
[1]
This is not the preferred method for making external links! But you can use it sometimes, for example on research pages where you prepare materials and you aren't yet sure whether you are going to use this link in the finished page that comes out from your research.