A paragraph is a group of words put together to form a group that is usually longer than a sentence. Paragraphs are often made up of many sentences. They are usually between four to eight sentences. Paragraphs can begin with an indentation (about five spaces), or by missing a line out, and then starting again; this makes telling when one paragraph ends and another begins easier.
In most organized forms of writing, such as essays, paragraphs contain a thesis statement. This thesis statement of the paragraph tells the reader what the paper will be about. The intro is used to give basic knowledge about the thesis. The body paragraphs are used to tell why your thesis is relevant. The thesis contains the main idea about the body paragraph. After one has completed an essay, one must close with a conclusion which restates the main idea.
A pilcrow mark (¶) is sometimes used to show where a paragraph begins.
Paragraphs are important to essays, papers, columns, whatever you are writing. Paragraphs help separate ideas and let the audience know when you change partial topics. Each paragraph has maybe an average of 3 - 7 sentences, depending on the topic and how much information is required. But it is usually 3 sentences long.