How is Hahirt a tragic hero? What is most tragic about him?

I'm guessing you mean Hamlet. I think the main one, and he has a few flaws, is his indecisiveness. Hamlet spends the bulk of the play thinking and pondering and being a big chicken. He endlessly debates everything from revenge to the meaning of life. When he finally gets to revenge it is convoluted mess but he gets the job done. Oh, he also loves his mother a little too much but that's a different flaw!