Hi Hira,
"Really" is a qualifier that is only to give emphasis when using slang. In academic English writing, it's not even permitted because it carries no meaning, only emphasis.
(1) "I sure am" and (2) "I am sure" have two different meanings.
(1) "I sure am" means the same as "I really am." Another way to say that (but it's never used) is, "I 100% am." For example, if someone asks you, "Are you Hira?" You could reply, "I sure am," or you could just simply say, "I am." Again, "sure" in this case is only for emphasis.
(2) In the statement, "I am sure" means "I am certain," which also means "I know."
I hope this clarifies.
Dean
