I had my fisrt shot on one a couple of weeks ago.
I must admit that since seeing a young French kid go arse over breakfast and really hurt himself on one about 5 years ago I've been a little bit cautious!
Anyway - my brother & I hired a couple out one day whilst we were away as the surf was flat. Took us about half an hour to figure it out but it's bloody good fun when you do.
The trick is to run along and throw the board forwards as you are running, then take a flying leap and attempt to land on it and keep your balance. If you get it right, you skim along for ages. If you get it wrong as we mainly did then you end up on your arse in front of a crowded beach.
We found the shallower the water you fling it into the better, so wait until a wave is creeping right up the beach about 2 or 3 inches deep and that's your green light. You then run along the beach rather than into the sea.
I've seen people who know what they are doing fling them at oncoming waves and do jumps etc. I think it's harder than it looks!!
Another thing - it's damned good exercise all that sprinting around!!
And it really, really hurt s when you fall - I still have a large scab on my left shoulder.....