Communication is a word that is so often used without thinking.
Many people see it as simply the means by which ideas, infomation, etc. are passed on to other people. How people communicate has a large impact on trust. For the most part, through interaction with others. How things are done, what the group norms are, what one's role is, even who one is in the eyes of others are all enacted through communication. Much of this cultural indoctrination is communicated implicitly.