CBT is based on a simple but powerful principle: the way you think about things shapes how you feel about them and how you behave in response. When thought patterns are distorted, skewed toward worst-case scenarios, self-blame, or catastrophizing, the emotional and behavioral responses that follow are distorted too.
CBT helps you identify those patterns, examine whether they are accurate, and replace them with more realistic ones. That sounds straightforward. The skill is in the application, which is why it requires a trained clinician.