Why are you the best candidate for the position you are applying for?
Because I have most of the skills that you need, and am easily trainable for the rest.
How your past personal and professional experience make you a quality candidate for the position for which I am applying?
Internal candidate is someone who already works for the company. This term is typically used when an employer is considering filling a position with someone who is already an employee, i.e. "The position is no longer available as we've filled it with an internal candidate." If you're applying to a company, you would be an external candidate.