Complex sentence: Rudolfo teaches Marietta how to handle the strings of the marionettes and then, to disguise Marietta as a boy, gives her boys' clothes to wear--following which Marietta and Warrington discover that they are falling in love with each other.
Split into simpler sentences: Rudolfo teaches Marietta how to handle the strings of the marionettes and then gives her boys' clothes to wear, to disguise Marietta as a boy. It is then that Marietta and Warrington discover that they are falling in love with each other.