A beanie is a type of soft hat with no brim that is worn to keep your head warm in cold weather. Beanies are often knitted.
A crown is something that royalty and deities wear on their heads. Crowns are used to signify that the wearer is someone special, and might hold special power. Crowns are usually made from precious metal and are studded with jewels, but they can be also made from simpler materials like wood, flowers or leaves.
Fascinators are small, decorative pieces of headgear usually worn by women. They are usually very pretty, and are worn to special events like weddings and to the racetrack.
A hat is a piece of clothing that is worn on your head. Hats come in all different styles, from helmets that protect you if you fall off a motorbike, big shade hats to keep you cool when you are outside, through to pretty hats that ladies wear that don't do anything other than look good.
A helmet is something you wear on your head to protect it from getting hurt if you fall. You should always wear a helmet when you are riding a motorbike or bicycle. People who work on building sites also need to wear helmets so they don't get hurt from things falling from above them.
A hood is a part of another piece of clothing that goes over your head. Hoods are often seen on cloaks, some jackets or hooded sweaters.
A mortarboard is the headgear traditionally worn at graduation ceremonies.