What Is It? 

There are many definitions of psychological warfare.  This is one:     

"Psychological operations may be defined broadly as the planned use of communications to influence human attitudes and behavior ... to create in target groups behavior, emotions, and attitudes that support the attainment of national objectives. The form of communication can be as simple as spreading information covertly by word of mouth or through any means of multimedia.

A psychological warfare campaign is a war of the mind. Your primary weapons are sight and sound. PSYOP can be disseminated by face-to-face communication, audio visual means (television), audio media (radio or loudspeaker), visual media (leaflets, newspapers, books, magazines and/or posters). The weapon is not how its sent, but the message it carries and how that message affects the recipient."             

...."Today, Psychological Operations are a vital part of the broad range of U.S. political, military, economic and ideological activities used by the U.S. government to secure national objectives. The mission of providing Psychological Operations for the U.S. Military today rests with the U.S. Army's Civil Affairs and Psychological Operations Command at Fort Bragg, North Carolina."

The realization that psychological warfare is being used against us is a difficult pill to swallow.  It starts slowly with  creeping suspicions caused by cognitive dissonance - the disconnect between the reality you know versus the reality that is being presented.  The recognition of psychological warfare is earth shattering because it means erasing the belief systems of a lifetime and rewriting them in view of the new information.  However, once done, the tactics become easier to identify and resist.