After installing FreeBSD, one of the first things you'll want to do is update the system.

First check for and fetch any available updates:
freebsd-update fetch

Next install any downloaded updates:
freebsd-update install

If kernel components were updated then reboot the system. If only userland components were updated then depending on what was updated you may not need reboot.

To automatically check for these updates, add the following to root's crontab
freebsd-update cron
The cron command:

Sleep a random amount of time between 1 and 3600 seconds, then
download updates as if the fetch command was used.  If updates
are downloaded, an email will be sent to root

When you receive an email notifying you that and update was downloaded, login to the system and install the updates
freebsd-update install

If you would like to configure FreeBSD to send email notifications to an external email system such as Gmail, then refer to this article: Forward Mail to Gmail

To check version of both kernel and userland:
freebsd-version -ku

-k          Print the version and patch level of the installed kernel.
            Unlike uname(1), if a new kernel has been installed but the
            system has not yet rebooted, freebsd-version will print the
            version and patch level of the new kernel.
-u          Print the version and patch level of the installed userland.
            These are hardcoded into freebsd-version during the build.