Most Helpful Girl
I would define confidence as feeling beautiful/confident in your own skin and your own body. Not wanting to be anyone but yourself. Not caring about what other people think of you, just do you and be you. Don't worry about what other people think, be your own kind of beautiful
Most Helpful Guy
I figure if I can walk into any place, and I'm sure I'll have more between my ears and between my legs than the next 100 men who walk in, then I can be confident.
That works for me, but that alone won't actually display any confidence.
Looking confident is something else. Imagine that you own the world, or that you don't care who owns it because you'll do what you like with it. Stand straight, and don't walk around looking at the ground. Don't appear to be rushed or hurried. Look people in the eye when you first meet them, at least long enough to see what colour eyes they have.
Don't be afraid to express an opinion. You're entitled to it, and you don't have to agree with everyone. Even if your opinion horrifies people, that's their problem.
There must be more, but that will get you started.