Just over a week after he attacks, the govenor of Pennslyvania was appointed as Director of the Office of Homeland Security. It became a cabinet-level department a little over a year later with the Homeland Security Act being passed. Its main goal is to protect the nation from terrorism.
The USA Patriot act was passed by congress to increase government surveilance abd investigative powers. It faced some backlash from the public because of concerns over privacy rights.
Around two months after the attacks, Bush signs the Aviation and Transportation Security Act, which immplemented required screenings by federal employees. After a failed attempt to sneak a bomb insode of a shoe, TSA added screenings for explosives to strengthen security.