Answer:
Of course grudges are real. People hold grudges against each other all the time. There are probably at least a few people whom you hold a grudge against: people who bullied you in school, or a co-worker who made up lies about you, or a friend who betrayed you.
It's normal to hold a grudge against people who have hurt you. Everyone has held a grudge at one time or another.
If you're asking whether the curse shown in The Grudge movies is real, then, a curse and a grudge are not the same thing. In The Grudge movies, it was the woman's grudge against her husband that caused the curse.
I suggest you look up the word, "grudge" in the dictionary. It is an extremely common word and there is no excuse for not knowing what it means.