A full page of text with no visible breaks is hard to read. That’s why you break your ideas up into groups of sentences, called paragraphs. Each paragraph contains logically connected sentences about one main idea.
If your teacher asks you to write a paragraph on learning vocabulary words, you will write several sentences that describe how to learn vocabulary. Each sentence will add to the topic and will connect one to the other. The length of a paragraph will vary. Your teacher might require just three or four sentences to accurately describe vocabulary learning. Unless he’s a fan of James Joyce. Then your paragraph might need to extend for pages and pages.