Step 1:
#pkg install xf86-video-fbdev mate-desktop mate xorg
Step 2:
Add the following lines to /etc/rc.conf
moused_enable="YES"
dbus_enable="YES"
hald_enable="YES"
Step 3:
#pkg install slim
Step 4:
Add the following line to /etc/rc.conf
slim_enable="YES"
Step 5:
Create the following .xinitrc file in the user’s home directory and add the following line.
exec mate-session
Step 6:
You might have to configure slim by enabling the following line in your slim.conf file. Or if you are using bash enable it for bash.
login_cmd exec /bin/sh - ~/.xinitrc %session
Reboot