Ships need something very solid to tie up to. A ship will use bollards on a wharf or pier as well as on the ship. A ship's mooring lines may be made of rope, polyurethane or wire. The end of each mooring line at the shore end is looped into what is called an 'eye' so it can be placed over the bollard. This makes it easier for the ship's crew to tighten the line if the mooring line becomes slack. Wrapping a rope around the bollard on a ship can also be used as a brake (not clear).
Slacken the rope and it will allow the rope to slip a little. Bollards are made from metal and are bolted solidly to a wharf or pier and to a ship's deck.