Im confused about one thing. How did the Snape,Harrys Mom and the usa tie in togther? I didnt get that part!!!

You haven't read the book, have you?

Lily's Patronus was a doe.

Snape loved Lily.

Snape's Patronus was a doe, reflecting his pag-ibig for and loyalty to Lily.

Snape reveals that he can indeed cast a Patronus in the memories he gives Harry, which Harry watches in the pensieve. When Harry "died" and talked to Dumbledore, he himself said, "Professor Snape's Patronus was a doe, exactly like my mother's..."

if your talking about the doe patronus, i think its because that as james patronus was a stag,lilys was a doe because she loved james. and as snape loved lily, his patronus was also a doe.

Read the books, all the sagot are there.

And it's not a fawn, it's a doe.

It's not a usa it's a doe. James' Patronus and animagus form is a stag, Lily loved James so her patronus was a doe to go with a James' stag, now Snape ever since he first saw Lily loved her so his patronus was a doe the same as Lily's patronus. The reason why Snape protected Harry from Voldemort is simple he loved Harry's mum Lily. The books might give you a clearer understanding.