I need to write a small essay about history and legend.
This is such an interesting assignment! What I do not know is the kind of course you are writing this essay for or what text sources you might be expected to focus on. No matter what, you will probably want to focus on whether or not legends reflect history.
Discussing this issue means focusing on particular texts and particular history, since this is not something you can discuss in just general terms. To show that legends do or do not reflect history means that you must have examples of particular texts and examples of particular periods of history. Two legends that might be worthy of consideration are the legends of King Arthur or Beowulf. Both of these are part of particular periods of English history, and you will need to not only familiarize yourself with the legends you want to discuss, but also you will need to do some research on these historical periods.
Then you need to ask yourself whether there or not there is any evidence that the people described ever existed and whether or not the events described actually happened. To find out, you need to find out if there are any historical accounts of people and events. And you will probably want to find out if there is any archaeological record to show the characters from the legends or the events described.
Even supposing there is no historical evidence of these particular people and events, legends might still offer us glimpses of history, how people lived, what they ate, how they dressed, and what the customs were. Often it is possible to find sources that show that the legends are "historical" in this way. Alternatively, there might be historical evidence that shows the legends as being completely inaccurate in this way. For example, was the technology available to make the armor for those knights during the period King Arthur was supposed to have reigned? Or did someone come along afterwards and write these stories when such technology did exist? When we see a detail like this in a story, we call it an anachronism. An example of that might be a microwave appearing in a movie that takes place in 1940. Anachronisms show us that a work is historically unauthentic.
This is really very much like a compare and contrast assignment, I think. You are going to be examining how legends are different from and similar to history. Do your research, and try that approach. I hope you enjoy this assignment. I know I would!