What are skills I should have for welding?

I have been interested in welding for a while now but I'm not sure what skills I would need. I'm also not sure how one would start a career I know I'll go to a trade school for it but can I be working as a welder while I'm doing that? What's the hardest part of the job? What are the hours? I would also love to know more about underwater welding and what that entails.