I would like to start an online company selling clothing accessories. How does the taxation work? -

Do I need any other tax id other than the one for my state...or do I have to apply for an id in each state in the U.S. What about selling to Canada...the U.K...and other countries?

you just need a sales tax license from your state - every state is different in what is taxable - clothing is not taxable in all states - if it is taxable in your state, you only need to charge sales for sales that ship to customer IN YOUR STATE. out of state shipments are tax free (for now)