Hey Willie, I'm a BCU (British Canoe Union) Kayak Instructor and Open Canoe Senior Instructor (Level 2 and Level 4 Coach respectively now).
I'm happy to answer any questions you have specifically (if I can) but to be fair everything "alick" has said below is very sound advice.
If you're just going to go in the sea then get a sea kayak but if you want to play on rivers or lakes then you would be better to go for a plastic kayak. Sea kayak's tend to be fibreglass.
Be very careful in the surf in whatever boat you get, the waves have a much stronger effect on a canoe than on a surfboard and you catch waves much easier (due to yoru increased speed from a paddle). Even at the level I am now at, I am still not able to teach people sea kayaking, it is a seperate disaplain and this is because of the risks.
Personally I'd advise you to try freshwater paddling first....build up your skill and confidence and then try the sea. You'll most likely get wet a lot to begin with and fresh water is nicer than salt to be upside down in! lol
I can't echo "alick" enough when he says not to paddle alone until you know what you're doing and I also very strongly advise you join a local club.
You can pick up cheap plastic kayaks all over the place, things to check are that it has foot pegs/plates, what the wear on the underside is like (there'll be some but you don't want it too thinly worn), check that the cock-pit hasn't split anywhere around it, make sure the seat is very securely attached and that the nose and tail haven't been rammed into a wall to hard!
As time goes on (and please get somebody to be with you when you do this) you will want to use a spray-deck. You can get fancy neoprene ones or just normal nylon ones (they are like a skirt that you wear that seals around the cockpit) this helps to stop the water splashing in and getting you wet/wetter!
For a paddle you will be best with a cheap aluminium paddle with asemetric blades (each spoon end at 90 degrees to the other) and if you get the blades spoon shaped (rather than flat0 then make sure you get either a left or right handed one depending on which you are.... the person in the shop will show you.
Right...enough waffling from me.... Willie, feel free to ask me anything else you want to know....don't worry about it sounding daft mate

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If I've been too simple then tell me and I can switch the info up a gear....hate to patronise but also don't want to jargon over your head either!!!
