The short answer is "just plug it in, and you should be good." It really IS almost as simple as that
The longer answer is:
1. All "filesystems" (for example, every partition on your hard drives) are "mounted" (before you can read from and write to them).
2. The commands to mount and unmount filesystems are "mount" and "unmount", respectively.
3. The command to see what filesystems are currently mounted is also "mount" (with no arguments).
/dev/sda2 on / type ext4 (rw,errors=remount-ro,commit=0)
proc on /proc type proc (rw,noexec,nosuid,nodev)
none on /sys type sysfs (rw,noexec,nosuid,nodev)
fusectl on /sys/fs/fuse/connections type fusectl (rw)
none on /sys/kernel/debug type debugfs (rw)
none on /sys/kernel/security type securityfs (rw)
none on /dev type devtmpfs (rw,mode=0755)
none on /dev/pts type devpts (rw,noexec,nosuid,gid=5,mode=0620)
none on /dev/shm type tmpfs (rw,nosuid,nodev)
none on /var/run type tmpfs (rw,nosuid,mode=0755)
none on /var/lock type tmpfs (rw,noexec,nosuid,nodev)
binfmt_misc on /proc/sys/fs/binfmt_misc type binfmt_misc (rw,noexec,nosuid,nodev)
gvfs-fuse-daemon on /home/paulsm/.gvfs type fuse.gvfs-fuse-daemon (rw,nosuid,nodev,user=paulsm)
/dev/sdb1 on /media/My Passport type fuseblk (rw,nosuid,nodev,allow_other,blksize=4096,default_permissions)
<= In this example, I have a little Passport drive mounted on "/dev/sdb1"
4. I would encourage you to:
a) Run "mount" (to familiarize yourself with your filesystems)
b) Identify your USB drive
c) Try "unmounting" it (so you can safely remove it)
d) Try plugging it back in (to verify it remounts itself automatically, and correctly)
'Hope that helps