When I say flawed characters, I mean that the character isn't perfect. Have you ever read a book where the main character was just too good? Too perfect?
Characters need to have vices. A temper, snappy attitude, bossy attitude; all of these are flaws. A character needs flaws for it to appear more human, so the reader will actually care about what happens to him or her.
A character needs to make mistakes, too. A wrong decision, a painful mistake; these are also things that need to be used in order for a character to seem human.