From a Southwest Airlines employee....

"Welcome aboard Southwest Flight XXX, to YYY. To operate your seatbelt, 
insert the metal tab into the buckle, and pull tight. It works just like 
every other seatbelt, and if you don't know how to operate one, you 
probably shouldn't be out in public unsupervised. In the event of a 
sudden loss of cabin pressure, oxygen masks will descend from the 
ceiling.  Stop screaming, grab the mask, and pull it over your face. If 
you have a small child traveling with you, secure your mask before 
assisting with theirs. If you are traveling with two small children, 
decide now which one you love more."