Naval boarding is to come up against, or alongside, an enemy ship to attack by placing men aboard the enemy ship. The goal of boarding is to capture, or destroy, the enemy vessel. Larger ships carried specially trained and equipped sailors, or marines, as boarders.
A cutting out boarding is an attack by small boats, preferably at night and against an unsuspecting, and anchored, target. It became popular in the later 18th century, and was extensively used during the Napoleonic Wars. This heralded the emphasis on stealth, and surprise, that would come to dominate future boarding tactics. An example is the successful cutting out of the Hermione which took place at Puerto Cabello, Venezuela, on 25 October 1799.
In modern warfare, boarding by military forces almost always involves stealth, and usually takes place at night. It may involve the use of small submarines or submersibles, or inflatable boats, or by scuba divers. All involve scaling the sides of the ship. When stealth is not as important, helicopters may be used to carry troops to the deck of the ship.
Source: https://en.wikipedia.org/wiki/Naval_boarding