Links are a very important part of the web an allow us to navigate around the Internet with ease.
When creating a link to an external site I would always recommend making the link open a new window for the external site, that way the user will not “lose” your site, and will come back to it once they have visited the external site. For internal links I would keep the user in the same window.
It is best to keep links within context of the content you are writing, also make the link text meaningful rather then click here for example. This will help with your Google Search engine optimisation.
How to create a link :-
Write your content, then highlight the word or words you want to appear as a link. Then click on the chain icon 
(10th Icon on the top row of the editor).
If creating an external link, add the URL (web Address) of the site or page you want to link to. (Include http://). Give the link a title, this is what appears when the link is hoovered over.
Tick the Open Link in a new window box.
For internal links, you can search for the page using the search and just select the page you want to link to.
Then click ADD LINK
and Update the page.