Can someone explain the technique used to shade?
Here is a website that may help you Noni. There is no real "technique" to shading as everyone may do their own shading a bit different from the next person. The second title on the list "Acrylic Basics for Beginners" has a ton of information that will be useful to you.
Here is a link that might be useful: Acrylic Painting
Think you are asking about floating......here is a site
that may help you. There are some that are illustrated...
will try to find them for you.
Good luck and enjoy,
Here is a link that might be useful: Tole floating/shading