Security culture is simply put as a set of rules that a community of people share to reduce and possibly eliminate the risk of exposure, subversion, and prosecution. Some practices of security culture would include rules such as never mentioning an action after it has already taken place, using secure channels of communication such as pgp encrypted emails or dark server hosted chat systems that are encrypted as well. Another important practice of this ideology is understanding laws, and how the legal system works which also includes all processes when someone is arrested. Knowing such things is key so that you do not make a mistake which could result in you going to jail for a very long time, and others going there with you.
One thing that I have always found overlooked in many cases where a group was infiltrated and ultimately destroyed, substance abuse was a key factor. Drugs make people paranoid, unpredictable, and more likely to cave into pressure from law enforcement. Many activists including Walter Bond mention how important straight edge is to such a movement, and they couldn’t be further from the truth. Anyone who has watched the documentary “If a Tree Falls” will understand this point completely.
Although I could go on all day about the importance of security culture, I will leave it at this for now, as we have so plenty of time in the future to cover all sorts of methods of security and how to best practice them, as well as handle various situations that could arise if someone you know is not following these practices.