Nope you don’t “need” to form a business entity to sell online, but you “should.” Forming an LLC makes things easier and safer for a business owner. It’s easier to have an LLC because you can avoid commingling your personal funds with business funds; by forming an LLC, you’ll have the chance to open up a bank account for the LLC. It’ll make things safer in the event that anything goes awry. By forming an LLC, and abiding by the necessary formalities for maintaining it, creditors will be unable to touch your personal assets if you’re ever sued or the business goes bankrupt. Obviously no one opens up a business thinking that it’ll go belly up, but it’s better to be realistic than optimistic when it comes to legal protection.