The rising action of a story usually takes place after the occurrence of some kind of inciting incident, and it ends with the story's climax. The inciting incident is some event that initiates the story's main conflict between the protagonist, or the main character, and the antagonist. The antagonist can be the main character themself, another character, nature, or even society.
The rising action, then, is constituted by any development of the conflict between the protagonist and the antagonist. Rising action is not to be confused with exposition, which is the revelation of any background information that the narrator might provide about the setting or the characters in order to help us understand the story and its messages more fully. Exposition can be offered right at the beginning of a story, or it can be sort of sprinkled throughout.
The rising action ceases with the climax, which is the moment of the most tension in the story; the climax can also be a kind of turning point. It is when we see either the protagonist or the antagonist gain ascendancy over the other. After the climax comes the falling action and, eventually, the denouement or resolution—the tying up of any loose ends and the eventual closure and ending of the story.