An essay is a piece of writing that

An essay is a piece of writing that is several paragraphs long. An essay, just like a paragraph, is about one topic. Since its topic is broad, the essay is divided into paragraphs, one for each major point. To tie all the parts together, an introduction is added to the beginning and a conclusion to the end.
An essay has three parts:
1. An introduction
2. A body (one or more paragraphs)
3. A conclusion
The introduction has two parts: general statements and a thesis statement. The general statements give the reader background information about the topic of the essay. These statements should get the reader interested in the topic. The thesis statement introduces the main idea of the essay. It is just like a topic sentence in a paragraph. It states the main topic and tells what will be said in the body
paragraphs. The thesis is usually the last sentence of the introduction.
The body of the essay consists of one or more paragraphs. Each of these paragraphs has a topic sentence, supporting sentences, and sometimes a concluding sentence. The body paragraphs support whatever is stated in the thesis statement. The body paragraphs are similar to the supporting sentences of a paragraph.
The conclusion is the last paragraph of the essay. It summarizes the main points discussed in the body or restates the thesis in different words. It also leaves the reader with a final comment or thought about the topic.
Transitions or linking words are used to connect the paragraphs. These are just like the transitions used in paragraphs to connect ideas between sentences.