I got a question about this, so I thought I’d post the answer here. To add a link in the editing window, select the text, and then click on the link button (looks like part of a chain) and paste in the URL. If you have .mp3s, you can upload and link them in a single step using the Add Media dialog. The text of the link needs to be put in as a “Title” there.
Also, here are the UK “t”s I played in class – they are all from the “Sound comparisons” website.