Hey Jan,
Start by checking out the publishers' web pages. All of them include guidelines for submitting a proposal.
Look at the kind of books that each publisher puts out and decide which would be the best fit for your idea.
Do a bang up job on the proposal. It's your introduction to the publishers. If it seems like too much work then you're probably more interested in being an author than being a writer. Writing a good book is a lot of hard work.
Submit to only one company at a time. Be ready for rejection, but keep working on your idea so that the next proposal can be even better.
Don't expect to make a ton of money. If the book is a best seller that's all cool, but most are not.
And finally, for heaven sakes, what are you waiting for? Get busy!
Beth
http://www.applewd.com/blog/