You know the big passenger ships like the Mayflower?How did people get on them?Was it the same as today or did they use row boats like l see in movies sometimes?

Gangways. Old as time.

They put wooden boards from the dock to the boat and walked onto the boat.

They built a dock the same height as the boat as it sat in the water. Then they used a plank/bridge to cross over. Rope ladders could have been used as-well, but generally people did not ride dinghies up to passenger ships.

or the ''gang-plank'' and then there were stairs and docks.. and ladders.