To "dare to ___" means to do something, even though it's dangerous, risky, or might get you in trouble.
In the example at the top of this lesson, the king says he will kill everyone who "dares to" oppose him. He thinks that it's crazy for anyone to oppose him, because he is so powerful.
Here's another example of "dare to ___". It's a common inspirational quote:
Dare to be different.
This means that you should be different from other people, even though you might get in trouble or get made fun of for it.