If a person under 18 decides to open a business and inorder to get inventory they need to sign a contract or agreement for the inventory?

With regard to contracts, the answer depends on what the party with whom you are contracting requires.  Contracts are agreements; they are voluntary.  For example, if the bank, or landlord, or supplier, or insurer, or anyone else requires signatures from you, your parents, your grandparents, and the family dog, you have the choice of (i) either obtaining all of those signatures, which will obligate all signatories; (ii) not contracting; or (iii) finding another source for what you need who won't impose such stringent requirements.  If the bank only requires your signature, then you will only have to provide your signature.  However, it is extremely doubtful that any business with whom you wish to contract will accept just your signature, since minors have the option of cancelling contracts they have entered into.  Any person or entity contracting with you will want at least one party who will be bound by the contract to sign it. You don't need to be an adult to have a social security number, and I believe that is the only type of tax registration you will need to do for a sole proprietorship, although you may need more if you have any employees.  Please don't rely on this; check with an accountant. As for a business license, I'm not sure what business you are entering into that requires a license, but you should check with the licensing authority will issue a license to a minor, or if you can operate such business on someone else's license.  If the business has to be licensed, I suspect that the answer to both of these questions is no.