Paragraphs consist of (at least) three sentences: the one that introduces the topic, the one that expands on the topic, and the closing sentence (think of it as a beginning, middle, and end—microscopically):
John was my brother. He was five years older than me. I loved him.
Dialog is a paragraph—meaning when a person speaks, they get their own paragraph.
“Where’s John,” asked Susan.
“In the store,” answered Marc.