An essay is a relatively short piece of writing dealing with any one subject. Sometimes it is essay writing how economy is related to common man, about a significant event, for example. Or you can be arguing about two contrasting viewpoints.
Lamb rambles, where you should be focused. Lamb’s introductions do not summarise his essays, yours should. Well, I do not think you should be boring! It tells the reader what to expect, and what to look for. The body or content of the essay will contain the points you want to make, with supporting arguments and evidence.
It must show the reader that you know your subject. You do this by explaining the subject to the reader. I look here at some of the other forms of writing that students are asked for, and how they relate to essays. Students studying some subjects may never be asked to write an essay. Parts of essays, like the summary, may also be forms of writing in their own right.