Bowman - trapping is a learned process. If you have never done any at all ever, at the very least you owe it to yourself to invest in a book or two. Or maybe better yet elicit the help of a friend who has some experience.
In case you didn't know, the 330's that are being talked about here are kill traps. When set properly, the critter that springs one is dispatched by the trap. But when a novice gets hold of one of these, especially one who hasn't invested in a setting tool of some sort, there exists the very real threat of bodily injury as has been pointed out. The leg hold traps and snares can be effective too and like Buck-Ridge was saying, can be set to drown your catch. But knowing exactly where and how to set these is vital to success.
I don't mean to discourage you in any way. You can get out there all by yourself and catch beavers. But getting out there with someone who has experience will put you way ahead on the learning curve.