Q. If everything in our life is fated, then why we must pray to GOD?
A. We pray to, and glorify God because He is deserving of it. Here in the material world we have forgotten God because we want to take His place as the enjoyer, controller and owner. When we realize our mistake by the mercy of His devotees, then naturally we will want to pray to Him to ask His forgiveness for our offenses and for strength not to again forget Him.
So we do have some individual free will, to turn to God or to turn away from Him. That free will is not interfered with by God, even if He may know how we will use it, He still gives us the right to choose.