FreeBSD has no GUI in its initial installation state. Here are a few steps to get the GNOME desktop up and running using the binary packages. Note that the packages could also be installed by using the ports collection. For easy configuration i prefer to use VIM but it needs to be installed first. Use following command:

pkg install vim

Installing the X Window System

This is needed by the desktop environment and can be installed easily by using

pkg install xorg

Configuring the X Window System

Now we need a few commands and edit to configure the system. As root do the following

vim /boot/loader.conf

add this line at the top:

kern.vty=vt

Installing GNOME desktop

It's time to install your graphical interface…

pkg install gnome3

after installation add this to /etc/fstab

proc          /proc       procfs  rw  0  0

now everything should be ready. Only one more step: add the following lines to /etc/rc.conf to start the desktop environment at boot:

dbus_enable="YES"
hald_enable="YES"
gdm_enable="YES"
gnome_enable="YES"

source: https://www.freebsdfoundation.org/freebsd/how-to-guides/installing-a-desktop-environment-on-freebsd/