The US has responded to terrorism in a wide variety of ways since the 9/11 attacks. Let us look at a few of the responses.
War. The US has engaged in two wars, one in Afghanistan and one in Iraq, that came about because of the 9/11 attacks. These wars were meant to destroy regimes that did or might provide safe havens for terrorists to operate from.
Nation-building. In these two cases in particular (as well as in Somalia), the US has been trying to use non-violent means to create stable governments and societies that would be less likely to cause radicalized people to turn to terrorism.
Covert violence. The US has also turned to a policy of using drones to covertly attack suspected terrorists in places where it would be hard to get “boots on the ground” to capture or attack those terrorists. This has been particularly common in Pakistan and in Yemen. (The raid that killed Osama bin Laden was a similar operation even though it did involve actual troops.)
Homeland security. The US government has been very zealous (some would say excessively so) in its attempts to prevent terrorist attacks within the US. This involves such things as aggressive law enforcement activities against potential plotters. It also includes the security measures that are so intrusive at American airports today.
All of these are important aspects of the American response to terrorism post-9/11.