It depends on state law

But most of the states require at least two disinterested witnesses. They have to sign after you publish and sign the will. "Publish" means you will have to announce to the witness in person that it is your last will and such. Notary public is not necessary and cannot be used to replace the witness. "Disinterested" means the witness can not be a beneficiary in your will in any form, either direct or contingent.