I like to surf in my free time.
I do as well.  I normally sure in the ocean, but sometimes I surf in rivers
Do you have to be standing on the board while riding a wave to be considered surfing?
Not at all.  A lot of people prefer body boarding, which you can do by laying on the board or just dropping down to one knee
Yes, i'm new to surfing, so I only surf lying down. What can you tell me about kite surfing?
There are a bunch of different styles.  There is freestyle, speed, course racing, among others.  I really enjoy it, but have only done it a couple of times.
What is the largest wave that a surfer has ridden?
I am not sure how big it was, but Garret McNamara broke the record.  His nickname is GMAC.
What are the origins of surfing?
History of surfing
The riding of waves has likely existed since humans began swimming in the ocean. In this sense, bodysurfing is the oldest type of wave-catching. Standing up on what is now called a surfboard is a relatively recent innovation developed by the Polynesians.The influences for modern surfing can be directly traced to the surfers of pre-contact Hawaii.
Polynesian origins.
The art of surfing, known as "heʻe ʻana" ("heʻe" means "to surf", and "ʻana"
boarding, when a surfer rides a wave on a bodyboard, either lying on their belly, drop knee, or sometimes even standing up on a body board. Other types of surfing include knee boarding, surf matting (riding inflatable mats), and using foils. Body surfing, where the wave is surfed without a board, using the surfer's own body to catch and ride the wave, is very common and is considered by some to be the purest form of surfing.
Three major subdivisions within stand-up