One of the best introduction videos I have seen, this one deserved its own page! Eric Heart is a prop builder and the Props Master at Triad Stage in North Carolina, and has a book on Prop Making that includes a section on thermoplastics (that you can see here).
This video includes information on working with Worbla’s Finest Art, moulding over a form, basic shapes, heating and shaping options, as well as attaching multiple pieces. It shows the process of creating a bull’s head over a positive mould.
You can see more introduction videos here!