Indoctrination (propaganda/public relations) is a process. It is done slowly, and carefully. It is a plan to sway opinion and beliefs. We are all susceptible to it, if we are unaware of how it is done.
Peer pressure, group think, conformity, mass media and education, are some of the methods of indoctrination. Indoctrination is not evil in itself, as we use it every day; for instance in teaching our children how to behave in public. We teach them certain norms of behavior through repetition, which is one method of indoctrination. It is the subtle indoctrination that we are unaware of that can harm us, by encouraging us to trust untrustworthy people, or into doing something that we might normally think is wrong.