freebsd-update is one of the ways available to update your FreeBSD system. In the simplest form, you can use it this way:
% freebsd-update fetch
% freebsd-update install
These two commands above, fetch and install updates for your release.
freebsd-update can also perform a rollback, be scheduled to fetch updates automatically and used to fetch new packages from a different release.
freebsd-update's behaviour is ruled by the /etc/freebsd-update.conf. You can specify which components you want to be monitored by freebsd-update (base system, kernel, sources...)
Though BSDs systems can be tough, this is an example of how easy things can turn out from time to time :)