To install NTFS-3G if you don't have it on, do:
# portmaster sysutils/fusefs-ntfs
 

Next, create a symbolic link from the newly-installed /usr/local/bin/ntfs-3g into /usr/sbin/:
# ln -s $(which ntfs-3g) /usr/sbin/mount_ntfs-3g

Modify your /etc/rc.conf to contain:
fusefs_enable="YES"

Provided you know on which hard-disk (based on make/model/capacity of the device) your NTFS partition resides, you can figure out it’s exact device node in FreeBSD:
# egrep 'ad[0-9]|cd[0-9]|da[0-9]' /var/run/dmesg.boot

aacd0 on aac0
aacd0: 953869MB (1953525168 sectors)
aacd1 on aac0
aacd1: 76315MB (156293120 sectors)
aacd2 on aac0
aacd2: 238475MB (488397168 sectors)
da0 at ahc0 bus 0 scbus2 target 0 lun 0
da0: <IBM-ESXS MAN3184MP F 5408> Fixed Direct Access SCSI-3 device
da0: 160.000MB/s transfers (80.000MHz DT, offset 127, 16bit)
da0: Command Queueing enabled
da0: 17357MB (35548320 512 byte sectors: 255H 63S/T 2212C)
da1 at ahc0 bus 0 scbus2 target 1 lun 0
da1: <IBM-ESXS DTN036W3UWDY10FN S27P> Fixed Direct Access SCSI-3 device
da1: 160.000MB/s transfers (80.000MHz DT, offset 127, 16bit)
da1: Command Queueing enabled
da1: 34715MB (71096640 512 byte sectors: 255H 63S/T 4425C)
GEOM_ELI: Device aacd1p1.eli created.

My NTFS partition resides on a 34GB IBM SCSI drive, da1s2. To confirm that /dev/da1 does indeed contain the NTFS partition, do:
# gpart show -p da1

=> 63 71096577 da1 MBR (33G)
     63 35664237 da1s1 ntfs (17G)
     35664300 35423325 da1s2 ntfs [active] (16G)
     71087625 9015 - free - (4.4M)

To mount the partition manually, do:

# ntfs-3g /dev/da1s2 /mnt/R1/tm01

Finally, add the appropriate line to /etc/fstab to have the NTFS partition mounted at the next system boot. For instance, my /etc/fstab contains:
 /dev/da1s2 /mnt/R1/tm01 ntfs rw,late,mountprog=/usr/local/bin/ntfs-3g 0 0