LLC

An LLC is a corporate entity separate from its owner(s).  Selecting an LLC as your business structure is probably the best choice because it may help you save taxes and protect your personal and business assets. 

Note that you also need a business license and a federal ID as well.   If you want to buy or sell wholesale, or sell retail in small amounts, you also need a seller's permit.

Finally, as discussed above, you will also need a state ein and a federal ein if you hire employees. 

Users of a assumed business name other than their last name or the corporation's or LLC's legal name.

 It takes about 1-5 business days to get it but it could be only one day or 10 days. It all depends on the government's processing capabilities at the time of filing.