The definition of 'sequence' is: an 'ordered' list of objects (read: events, feelings, impressions, textures, shapes, etc.). Like a set of objects, a sequence contains a number of elements. Unlike a regular set, order DOES matter. In art, sequencing can show the passage of time. It tells (shows) what came first, next and last. Examples of things that 'happen' in sequence: comic strips, a song, fading light, falling asleep.
Using speech (what most of us use) to convey these ideas is much different than showing them in abstract images. Your instructor wants you to make that leap, from verbal to abstract image. Even Journalism majors need these skills. Images are excellent comunication tools - where would we be without graphs and maps? Editorials frequently contain a graphic to help explain a concept more fully.
Don't worry - it gets better