A dock is the area of water between or next to one or a group of human-made structures that are involved in the handling of boats or ships (usually on or near a shore) or such structures themselves.
It is a structure that's made for bringing boats or ships to the shore and loading or unloading goods or passengers. The small dock behind your lake house might be mainly used for launching your canoe. You can also get the best services for custom dock construction via coastseawall.com/docks/.
The other main purpose of a dock is to expose the underwater parts for inspection, repair, and maintenance. The ship to be repaired is hence maneuvered into the lock. The gates are sealed posts in which all the seawater accumulated in the vessel is drained for better inspection and repairs.
Docks are specifically used to repair vessels that have met with accidents or broken down in the middle of the sea. A U-shaped structure called pontoons is used to salvage ships from mid-sea. These U-shaped structures are filled with water, which makes the dock go underwater helping the ship to sail. Once the ship is secured and brought to the repair area, the water is released, making the dock to rise up and exposing the parts of ship that are otherwise underwater.