If your self employed, do you have to be a company?

To write off stuff on your taxes? Like business expenses etc.? I sell stuff, and im planning on filing taxes this year. Id like to open an LLC but im a minor. Hows this going to work? If i dont file taxes will they tax my parents for my income? If i file taxes can i still writeoff business expenses? What about inventory costs? Someone told me i cant pay taxes only my parents. But my business just cant afford to be paying taxes for my parents tax bracket without making my parents money!