An H-1B visa has two parts to it-the visa petition and visa stamping. After your H-1B visa petition is approved comes the next part of H-1B Visa stamping where your visa is endorsed. A H1B visa stamping in the passport is needed for a foreign national to enter/re-enter the United States as an H1B worker. Your visa stamp is one of the requirements to prove that you have valid authorization to travel to the United States.
All H1B visa stamps must be issued by the U.S. consulate outside the USA situated in your home country and you must appear in person for the interview at the consulate. You will have to apply for the visa stamping about 90 days before you begin working at your new workplace.