What is essay?
What an essay is:
An essay is a written argument which consists of an introduction, a statement of a thesis, support for that thesis, and a conclusion. An analytical essay addresses an issue and employs a critical approach; to do this, it takes a stand on some issue and assesses strengths and weaknesses of the work or text under analysis.
The parts of an essay and their functions:
A thesis statement is a sentence which tells what you think about the topic of your essay. Your thesis statement should be a sentence that will prompt a response in a reader, or cause him/her to ask "why?" Your thesis sentence should also be a statement that contains the gist of your point of view on the subject you are going to write about.
Generally, a thesis statement will appear in the introduction to the essay, which is the first paragraph or section of the essay introducing your topic. Aim for a clear, strong introduction that sets out what you're going to say. Your introduction should be mainly the "explaining" part of your paper. You should be aiming to present your idea in the introduction (whatever it is, agreeing with an idea or disagreeing), and then explain how it generally works. You don't want to get into specifics yet; you just want to establish the direction in which your essay is going to go.
Support for your thesis will appear in the body of the essay, which is the "illustrating" part of your paper. In the body, you want to show how you know what you say you know, and to do this you are going to use examples. You should be as specific as possible. Give several carefully-chosen examples, or if you have few, provide very detailed accounts of them. If your examples are well-described, it will be clear to the reader that you have excellent reasons for believing as you do; thus you will have shown how you know what you say you know.
The essay will end with a conclusion, where you will "wrap up." In your conclusion, you are trying to show how what you have described and discussed is generally valid.
Checking the draft for completeness and high quality:
It is important to learn to edit your work; there are very few good writers who are not also good editors. Plan to spend some time checking your draft.
Check for clarity; you want to make sure everything you've written sounds like it makes sense and is reasonably correct. You should first read your essay over slowly to yourself (or even aloud) and catch any mistakes you see.
Edit out anything in your paper that seems to be going in a different direction to what you want to say. You don't want to contradict yourself.
Make sure there are smooth transitions between parts of your essay. You want each paragraph to follow from the previous one, so your whole essay flows along. There's a simple way to do this: make the last sentence in each paragraph reflect or echo the first sentence in the next. Try practicing this a few times.
Watch out for sentence fragments. Where sentences begin with If, Since, Although, When, etc., make sure that they are properly finished. For example, "Although my dog died. My cat is still alive." should be, "Although my dog died, my cat is still alive."
Divide up run-on sentences. Where you have two sentences run together, separate them with periods. For example, the sentence, "I go to The College of Staten Island I am thirty-three" should be "I go to The College of Staten Island. I am thirty-three."
Separate comma splices. When you have two complete sentences joined only by a comma, this is a comma splice error, as in the sentence, "I had no food for three days, I survived." Find ways to join the sentences in ways that show the relationship between them, such as, "I had no food for three days, but I survived."
Be sure that you don't end up with subject and verb disagreement. This happens when the subject and verb are in conflict, such as in the sentence, "The trees is beautiful." There is subject/verb disagreement between the subject (trees) and the verb (is) because where the subject "trees" is plural, the verb "is" is singular. It should read, instead, "the trees (plural) are (plural) beautiful."
https://csivc.csi.cuny.edu/history/files/lavender/essay.html