Your first assignment is to explore how CSMA/CD behaves under load. In particular, you should explore the relationship between offered load and throughput. You should explore both, the number of sources offering load and the amount of load offered by each source.
I have written a sample ns script that will help you get started using ns for this experiment.
Your report should be written up as a laboratory experiment (including sections on background, theory, hypothesis, results, analysis, and conclusions) and should be no more than eight double spaced, typeset pages, including figures and graphs. If you like, you may include your tcl script(s) in an Appendix.