To be self-confident is to be secure in yourself and your abilities. When you are giving a presentation or a speech, it helps to be self-confident –- or at least to pretend that you are.
Confidence is a feeling of trust in someone or something. To be self-confident is to have confidence in yourself. Self-confident people don't doubt themselves. This is usually a positive word: you can be self-confident without being cocky, arrogant, or overconfident. If you know what you’re doing, you have every reason to be self-confident.