Changing multiple fields at once

I am very new here, not a frequent Windows user, and using mp3tag on a Mac (I am using Wine). I have opened my directory of files, but my question is how do I change the value of a field of a number of files at once? The value is the same across all the files (I have a blank field).


see e.g this thread:

Marvellous! Exactly what I wanted, so thank you.