What methods do terrorists employ?

One method,if my understanding is correct, is to attack by surpirse or to kill as many people as possible. 
By doing that, the killing of numerous/millions of people, usually end on on planes, buildings... That type of stuff. 
They usually do bombing of large areas.
~Hope this helped :)

Im not exactly sure but:
- fear of arms and ammunition they cArry with them
- theyre often masked which instigates fear of the unknown
- theyre possibly popular for terrorist activities