Traditions is nothing more than an orientation. However this one is a bit more fun. You learn about the history of the company and the resort. You go on a little tour of the park and the backstage areas as well. You'll learn about some the behind the scenes stuff. It's kind of cool the first time you see it all. You also get acquainted with your fellow cast members who are attending traditions as well. Be sure to follow the dress code because from what I remember they were really strict about it. Also be prepared for a lot of walking. From what I remember traditions is like an 8 hour day, but also consider the fact you need to get there early and will be doing a lot.
Welcome To is where you get familiar with your department and learn a bit more about the specifics of whichever department you're going into. You get another tour of the resort but this time it's around the areas in which you will be working in. It's some what like traditions, but more applicable to your job. Welcome to is about the same amount as traditions I believe, it's been a while.
I don't remember much about California Story, just that it was about 4 hours long.