The relevant wikipedia diagrams can be found here:
http://en.wikipedia.org/wiki/Relativity_of_simultaneity#The_train-and-platform_thought_experiment
and here:
http://en.wikipedia.org/wiki/Light_clock#Simple_inference_of_time_dilation_due_to_relative_velocity
The following are my diagrams, copyright 2013 by Scott Reeves:
Diagram #2:
Diagram #3:
Diagram #4:
Diagram #5: