It's pretty easy to turn any of the text in your email into a link. First, highlight the text you'd like to turn into a link. Once you do that, click on the link icon in the text toolbar:
You'll now be given two options:
You can add multiple links to your email, but you shouldn't turn the entire text of your message into links. Think of links like whipped cream - pretty good on it's own, but even better when there's some pie underneath it.