Why and how did Al-Qaeda do it?
What were the consequences for Al-Qaeda and the rest of the world after the attack?
The reason Al-Qaeda attacked the United States was because the West constantly attacked Muslims in Somalia.
The aim of the action was to hit the United States as hard as possible. It was not by killing as many as possible, but by hitting them financially, militarily, and politically.
Financially: by flying into World Trade Center 1 and 2. The many jobs in and around the World Trade Center complex, which gives a lot of money to the US state, where some of the money is spent on military action in the Middle East.