List drives.

# gpart show # df -h

Name of my USB drive is da0.

If USB drive is mount, unmount it.

Delete partition table from USB drive.

# gpart destroy -F da0

Create new table and file system FAT32.

# gpart create -s mbr da0 # gpart add -t fat32 da0

Format the created partition.

# newfs_msdos -F32 /dev/da0s1