To make a hyperlink in a field, ensure that it is a "Rich Text" field (the default for new fields), switch to the Interact tool, and select a region of text within the field. You can then use the "Text -> Link..." menu item to create a hyperlink, which will be shown with a dotted underline. When you're finished editing, to make the hyperlinks "clickable" you must lock the field, by switching to the Widget tool, selecting the field, and choosing the "Widgets -> Locked" menu item.
Fields emit a "link" event when a hyperlink is clicked, which you can intercept with a script to do as you please. If you don't write a script, the default behavior is to go[] to the text you provided when you created the hyperlink. If that's the name of a card, it will navigate to that card. If it's a url like "http://google.com" it will ask the web browser to open a new tab.
Hope that helps clear things up!