Embedded below is a 1 minute and 34 second YouTube tutorial from both the sender's and receiver's point of view.
To find out more about Gmail's confidential mode click here.
One thing to point out, I did read that if you do not see Confidential Mode - try going under settings and then toggle conversation view to on. I myself did not have to do this - but read a few places that some users did. Not sure why or if this would make a difference - just passing on.