Is it legal for a Company to hire you and not inform you of your salary/benefits until you start your job?

Sure its legal...

But who accepts a job before they know what they are going to be paid or what the benefits are is the better question.

Because it's a really good opportunity with a well known company and I just graduated from college and I'm looking for a good full time position.

How do you know it's a great opportunity if you don't know any of this... you did get an offer letter from them didn't you?

Personally I would never blindly accept a job without knowing any of this stuff... and if they did extend you an offer, its always going to be in writing. Never purely verbal.

Are you certain you were offered a position? Just being interviewed doesn't mean you have an offer... and nothing is official until they do send you that letter. And that letter will also specify exactly WHAT position the offer is for.

Just trying to make sure there isn't a chance of a misunderstanding here...

I've been through more than a few employers since I got my degree 30 years ago. So I've done a LOT of interviewing... and even interviewed a few people myself over those years.

They gave me the position and I start jan 3rd.. They just are finishing up paper work and they will let me know. I just wanted to know if this is normal for some company's to do?

Legal yes... normal no.

I've always known what the job paid before I was expected to give an answer.

I agree, this is not normal for a "well known" company. Even small companies will make a formal offer in an offer letter. No company will make an offer without indicating what your salary will be, and accepting a position without such information is not smart on your part.

I have serious concerns that you were made a bonafide offer. The good news is that, since they did not give you a written offer, then you can back off. I would contact the company immediately and explain to them, that you can't really accept a blind offer, that you need to know what your salary will be and what benefits are offered before you can formally accept.

Maybe you said you would work for any amount?
Anyway, you can be eager and dedicated and still businesslike, protecting your own interests.
If I were that well known company, I would not think highly of someone who doesn't even ask at some stage of the interview process.
It makes you sound like you would 'give away the company,' telling clients you (the company) will agree to anything. It makes you sound too naïve too.

How did they make you this offer, has it all been email or is here formal letters, interviews in person and so on.

It is not business like and very unprofessional to hire you without you knowing the pay. Perhaps it merely pays min wage for a starting position. Perhaps you on a application said you would work for >>> and that is what they will pay you.