Well there are a few different types of kayaks. The first is a closed sit inside or sea kayak. This is the kind most people think of when it comes to kayaking. You sit inside, and have a skirt that goes around your waist area. This keeps water from getting in, and you will see people doing rolls in them, which is going under the water upside down.
Then there is the growing in popularity, sit on kayak's deck. As you can guess, you sit on top of the kayak. If you tip, you fall out, although I have heard of people doing rolls with these if they use knee straps. You will get wet in these. I like them because you can hop in and out of it. Mine is also made for stability so I can stand up in it.
Then there is the "hybrid" kayak. You have a larger opening to sit in, typically no skirt, and a large deck. I really cannot tell you much about them.
Then you have a canoe. A canoe you can sit deeper in the water like the sea kayak, you have no deck, and you have higher sides. Typically though you have a seat in a canoe that you sit higher up. I think a canoe may be better for carrying larger, heavier loads. Canoes can take on water, and tend to catch the wind.