This section provides security configuration advice for site administrators and includes both "things you should actively do" and "things you shouldn't do". The order of chapters is an attempt at identifying the priority of the configuration based upon the likelihood that it will be helpful and the potential benefit/harm of the configuration.
There are a number of contributed modules which can help with security, not all of which are documented in this handbook. Among those modules is the Security Review module which provides an analysis of your security configuration.
You can also read documentation for writing secure code and about the security implications of translations from localize.drupal.org.