Your personal brand is the impression that you give others. How you dress, what you do, your personality; these are all things that make you, you.
Think about buying a new mobile phone or ordering a pizza, do you have a favourite company or product that you pick every time? It's the same with your friends and the people you meet. You're influenced by the impression they give you, and they're influenced by the impression you give them.
Within the first minute of meeting someone new, they'll form opinions of who you are based on your appearance, body language and personality. This first interaction is an opportunity to stand out to a potential employer or with anyone new you meet.