"Confidence" is a quality that people sometimes have. It means feeling good about yourself and your abilities. You can use the word "confidence" like this:
A: I'm not very good at this.
B: No, you're doing a great job! You just need to build up your confidence.
Most people think of "confidence" as a positive quality. There are some other words for similar qualities that are negative. For example, you might describe a person's high opinion of themself as "arrogance":
Everyone likes confidence, but arrogance is really unattractive.