Characters travel down the road projected by the plot — a string of events that takes them from the beginning of the story to the end. Like road builders, authors connect section after section of their concept so that characters can travel along them to reach their destination. But usually that traveling doesn't go smoothly: conflicts — head-on collisions of events — often beset and besiege the protagonist. These conflicts can be internal, within the main character, or external, issues the main character has with another person, animal, object, a force (like the force of time), government, or nature.
When adding conflict to your story, don't overload characters with too many quirks or problems. You don't want to add so many conflicts that readers — and characters — can't catch their breath.
In Emily Brontë's Wuthering Heights, Heathcliff is continually at war with his feelings: with his love for Catherine and his jealousy of those she gives her heart to. In L. Frank Baum's The Wizard of Oz, the trigger event is a tornado that takes Dorothy far from her home and leaves her to face a tin man, a scarecrow, a witch, a wizard, and a lion as she attempts to return home.
Conflict is the basis of the drama in a story, and what pulls readers in emotionally and gets them to turn the page. A well-paced and well-developed plot should contain enough instances of conflict to produce tension and emotion in a continual escalation, but also times of calm when things go more smoothly.
Here is a simple plot, provided by Gary Provost, teacher and author, in How to Tell a Story:
Once upon a time, something happened to someone, and he decided that he would pursue a goal. So he devised a plan of action, and even though there were forces trying to stop him he moved forward because there was a lot at stake. And just as things seemed as bad as they could get, he learned an important lesson, and when offered the prize he had sought so strenuously, he had to decide whether or not to take it, and in making that decision he satisfied a need that had been created by something in his past.