In 1919 he went to join this party and when he got there he saw a man speaking, adolf thought what he said was wrong so they had an argument until adolf won and he gained respect for his political skills. With that he saw an opportunity.
With this skill he went to speak to others and let them join in this party, soon it grew and there were ads around town and many people joined in and supported this party.
After they changed the name from German workers party to National Socialist German Workers' Party (Nationalsozialistische Deutsche Arbeiterpartei or NSDAP) called for short, Nazi.
And the rest is history, this how he gained his power and formed nazi.