A harbor, also spelt harbour, is a sheltered body of water that is deep enough for ships to dock and unload. Harbors are generally an inlet or bay surrounded by land.
A harbor is also a term used for any safe place, or can be used as a verb to mean keeping something or someone safe, as in "he was harboring a known criminal".
The Jolly Roger is a flag with a skull and crossbones that was traditionally flown on a pirate ship, although many pirates would just fly a plain black flag.
The reason pirates wanted people to know they were pirates was just to frighten the crew of other ships into giving up without a fight.
The Jolly Roger in the picture is being flown along with some other modern flags.
Pirates sail around the oceans, stealing from other ships. This is called piracy and is still common to this day. The captain of a pirate ship was typically the strongest fighter and one the men could trust. Pirate ships would often take on outcasts from society to join their crew.
The skull and crossbones design on the pirate's hat is known as the Jolly Roger. The pirate in the picture has most of the features that pirates in modern movies and cartoons have: a parrot, a wooden leg, a hook hand and an eyepatch. In reality, with the conditions found on ships in the 1600s, a pirate that suffered such injuries in battle would have died from infection.