Can you translate that into laymen’s terms please.
According to biblical commentators, ancient Israelite cities were encircled by defensive walls, and their gates were the locations of the markets and public gathering spots, where the elders, judges, and king held court. So the "gates" were not just the physical doors, but also the powers of a city.
So the "gates of hell" means the "powers of hell." The powers of hell want to destruction of the Church. So the passage means that the powers of Hell will not succeed in destroying the Church.
I do not think this means the Church is entirely invincible in every situation. History shows that this not so. But in the final instance, there will always be a remnant of the Church. It will not be finally and totally wiped out.