I love surfing out in the waves. 
I have never done it but I think it is odd unlike swimming it is a surface sport, that requires you to stay on top of the water
yes, its like skateboarding on water really. I love it when I just get an entire out there. 
my understanding is that the best waves for surfing are in the ocean, but you can also surf in lakes and rivers
I have only surfed on oceans but lakes and rivers would be fun. The best waves are on the north shore. 
artificial waves can be used too like from boat wakes or wave pools
yes, people skiing from behind the boats. 
the word surfing refers to the riding of waves regardless if they are on a board or not I guess that is where the term body surfing came from
very interesting fact, I wonder when this became popular?
I am not sure but modern day surfing usually refers to riding waves standing up on a board, or stand up surfing as it is sometimes called