FreeBSD, format and mount your USB drive

• after insert your usb drive, check where it is by using /dmesg, i.g. /dev/da0
  
• you might need to format it so FreeBSD can recognize it
• you can use newfs or newfs_msdos to format your drive, if you want windows to recognize it too, try newfs_msdos -F32 /dev/da0. this will create a FAT32 filesystem
• you can use fdisk to check the partition first, i.g. fdisk /dev/da0
• after you have format your filesystem, you can mount it now. i.g. mount /dev/da0 /mnt, or mount_msdosfs /dev/da0 /mnt (/mnt is a directory you create)

Usually, simply use mount command will do the job. If not, make sure you have the right filesystem and mount the right device to the right place.