Blessings are good things from God which bring us joy. They encourage us to have more faith in Him.
Curses bring evil (sickness, tragedy, or other problems). They cause delays or even failure in our lives.
A stronghold comes from wrong thought patterns of lies that we develop from deception. The main vehicle bringing both blessings and curses are words—whether spoken, written, or merely uttered inwardly. Deception comes when we believe a lie, then deception leads to strongholds.
Jesus took the curse of the law on the cross and He makes us a new creation when we believe in Him. There are steps to freedom and release from curses and strongholds.
Our highest blessing comes by faith in Jesus, through grace, bringing forgiveness and eternal life with Him in heaven.