Surfing refers to two activities: first, the use of a surf board (a varnished, smoothed, hydrodynamic board) to ride waves in the ocean, and second, the perusal of the internet for recreation. Originally, native islanders of the Pacific used long heavy planks to ride the surf, and they were observed by the British in the late 18th century. Surfing took off internationally when two Hawaiians popularized it in the early 20th century, and by WWII California became the center of the craze. Americans made lighter (hollow) boards and attached a rear stabilizing fin. Some boards were made of balsa, with internal ribbing for support; nowadays most board are made of fiberglass, which is cheaper and lighter than wood.
It takes some time to learn surfing, but it can be a very enjoyable sport. Outside of the tropics, surfers wear a wetsuit to keep warm.