This process is called hyperlinking. To hyperlink any text in your emails in your PR campaigns, all you need to do is edit your campaign (or create from scratch), then in Step 2, supposing that you already have a draft of your email/s including that text that you want to hyperlink, just find the hyperlink icon (refer to screenshot below) in the text box options (above each text box). Before clicking that, highlight the text/word that you want to hyperlink then click the hyperlink button (insert/edit link).
Then enter the target link in the URL field:
The Title is for what you want to show up when you hover your mouse over the hyperlinked text.