I know that false pretense have to do with a scenario involving someone who pretend to be someone else in order to obtain money..etc. But I get confuse with both of them
False pretenses are actions or behavior designed to deceive, in any capacity. When said behavior is used for financial or personal gain to someone else's loss, it becomes fraud, although different jurisdictions may have differing rules and definitions as to where the line of fraud lies.
Forgery is the making of fake items, especially documents of a legal nature.
This is a succinct statement of "false pretenses". To be guilt of false pretenses, you must obtain title to personal property of the victim, not merely possession.
The important distinction between possession vs. title is that the owner has to transfer ownership of (knowingly give) the thing, so if a bookkeeper makes false entries in the books and surreptitiously takes money from petty cash, that is not "false pretenses". If the bookkeeper gets the owner to give him the cash as reimbursement for alleged expenses incurred (when there were no such expenses), that is "false pretenses". There has to be an intentionally false statement about a past or present fact or state (but not a future fact or state). So, if the bookkeeper claims that he will have certain expenses but does not do the things, that is also not false pretenses (because he's making a false statement about what he will do, not about what he has already done).
Forgery, on the other hand, is making or altering a document so that it is false, with the intent to defraud. It need not result in actually obtaining anything, so a forged check is still forged even if it isn't cashed.