Dare means to have the courage to do something: "Would he dare to tell the true story?" It can also be used for a challenge: "I dare you to face the danger alone?" Daren't is a contraction of "dare not." I seldom hear this word used in English conversations where I live in Canada. If it is used in a sentence an example could be: "They daren't drive the car that they stole if the police are searching for them."

It's certainly a word ( daren't ) but to use it would be very strange indeed. I've never encountered it in my life. May I ask where you saw it?

To the best of my knowledgement there is a usage for it: 1. You use this word when for example challeging someone to make him(or her) go beyond their courage and do something: -For Example: Haunting house. Go inside if you dare. (Doing so you are a courageous person)