Look at the figure titled ``Examples for Plate Motion Problem (Problem 5)'', shown below:
The shaded rectangular boxes are meant to represent spreading centers, where the plates move away from each other.
The lines with black triangles on them are meant to represent subduction zones, where one plate dives beneath another plate. The triangles are customarily drawn pointing away from the subduction zone, on the plate which is overriding the other plate.
Straight line segments are meant to represent transform faults, where two plates simply slide past one another, without either diving or spreading.
The big heavy arrows are meant to represent plate motion that I tell you about. The skinny arrows are what I want you to draw in Homework 3, Problem 5.