Do I have to have an attorney to make a will legal?

Wills must be witnessed in a formal ceremony conducted by a notary.  The number of witnesses required varies from state to state.  They should also attach the state's self-proving affidavit, signed, witnessed and notarized. The problem with most self-written and many internet wills is that you don't know what you don't know and can easily omit something required to avoid the will defaulting to an heirship (which is more expensive and may not pass things the way you want) or something your executor will find useful or necessary (such as access to your online accounts) or something which will preserve benefits for a disabled beneficiary, etc.