The Essay: What is it exactly?
Essays are structured collections of ideas.
As you learn to write essays, you improve your skills at reading essays. And as you improve your skills as a reader, you (symmetrically) improve yours skills as a writer. Good writers read lots of good writing; good readers know a thing or two about good structure and technique. Reading and writing, we might say, are shades of the same colour.
Essays make points.
Perhaps you've heard of the classic five paragraph essay: one paragraph introduction, three paragraphs of support, one paragraph conclusion. This is a tidy way to introduce the idea of an essay, but it is not what an essay is, full stop. In the classic five paragraph essay, you state a point, support the point, restate the point as supported. That is, you articulate and argue for a point.
Though here I'll advocate a less-structured approach to composition, two things are worth noting. First, it's extremely valuable to be able to whip up a five paragraph essay, especially in communications or business contexts. Second, a series of activities here ("Writing is rewriting") will lead you, more or less, into this structure -- though you won't be limited to the structure. Choose your level of involvement.
Of course, there are lots of ways to make points, and essays need not take any particular form. For example, academic essays often include a "survey of a literature" in which the writer paraphrases prior research in the same area. This is meant to provide context for the writer's thesis. Personal essays, memoirs, and the like might start with anecdotes to catch a reader's attention and illustrate the essay's theme. Persuasive essays often start with a bold assertion, then collect evidence in favour of that assertion, while also refuting competing assertions.
Notice that we've only mentioned length when talking about the five paragraph essay. There are really no limits. For example, John Locke's Essay Concerning Human Understanding spans four volumes. Generally, you write as much as necessary to make your point clear and strong, and this can vary widely depending on your topic. (Human understanding is a broad enough topic that we might forgive Locke's rather lengthy treatment.)
As a contrast: the purpose of an essay, in general, is not to tell stories. You might think the personal essay or memoir is an exception, but their purpose makes the difference. It's not simply storytelling; in the memoir, the writer breaks free of the narrative and makes their motivation clear.
In reality, there are no rigid rules for what can and can't be an essay. Here has been a quick survey of the landscape, and surely as you proceed, your view will change.
Now, as we've said, writers have to be motivated when they write essays; they have to want to make a point. Have a think on that and add your thoughts to the discussion forum. What kind of point would you want to make in an essay? Political? Scientific? Express an opinion? Elaborate on a concept? How would you characterise your point: simple or complex? Compare you thoughts on essays to how you tell stories or how you try to persuade someone of your point of view.
Next we'll have our first external reading. Consider the point the author tries to make; consider his motivations. Discuss this and other prompts in the forum.