Absolutely, you will need a business license. Especially if you plan to receive or exchange money under that name. It is otherwise illegal to operate a business without one.
Unless you are operating a business that carries liability you may consider a Limited Liability License (LLC). If you have multiple businesses under one name is also consider an LLC.
Overwise a simple Business License otherwise known as a DBA (Doing Business License) will do just fine and typically lasts 8-10 before it will expire. The difference in price is that the LLC could run you upwards of $300. The cost of a DBA could be anywhere from $10-$20.
With any business license, you'll get a Tax Indentification Number (TIN Number) which works similar to an identification number unique to your business (similar to a Social Security number for your business) that you'll need to keep confidential. It will come in handy when it's time to do taxes. Apply for your business license, by contacting your local county clerk's office's website.