Common structure elements to look for when reading your assignment:
If the above are not in your assignment, look to see which citation format your instructor requires. MLA, APA, and Chicago styles all have guidelines on structuring your paper. Be aware that some professors do not have strong preferences as long as you are consistent and fully answer the assignment. Some professors are very specific and will deduct big points for deviations.
If your instructor has told you not to consider sources outside of those specified in the assignment, then you should follow that instruction. In those assignments, the instructor wants to know what you think about the assigned sources and about the question, and they do not want you to bring in other sources.
General Writing Guidelines