Essays written in English are divided into paragraphs. A good explanations of paragraphs and their structure can be found on the website of the University of Essex.
One of the most important characteristics of paragraphs is that they tend to centre on ONE TOPIC. This is usually introduced in the first sentence, also called the topic sentence. You can find examples of topic sentences on the website of the University of Ottowa. After introducingit in the first sentence, a paragraph then expands the topic.
Examples of typical paragraphs from different subjects can be found in our subject-specific writing section.
Information on paragraph structure with examples from BNE can also be found in our vidcast (ADD VIDCAST ch. 2 2.07 to end).