I demonstrate the similarities and differences between films and books

Well usually, a film is made from a book or follows a books script. A film can sometimes follow a book exactly or it can change it completely. Take the book "Perks or being a Wallflower" and its film. The film excludeds a number of parts from the book, making new parts instead.

in short

Similar: They both follow a script and they both are looked over usually by the original author.

difference: Movies are usually shorter than books or longer in some cases.