How do I embed an mp3 audio in a text box?

Upload the mp3 file to Resources.

See How do I upload files? for more information on uploading.

In the text box, position your cursor where you want to embed the mp3 audio file.

Click Insert/Edit Movie.

This displays the Movie Properties dialog box.

Click Browse Server.

This displays the Entity Picker dialog box.

Select the mp3 audio file you want to embed in the text box.

This returns the display to the Movie Properties dialog box with the URL of the mp2 audio in the box marked URL.

Set the Height to 35, and then click OK.

This returns the display to the text box with a place-holder for the audio marked "Movie". When the text box item is published the embedded audio player will be displayed.