sudo apt-get update

sudo apt-get install samba samba-common-bin

Configure the software

sudo nano /etc/samba/smb.conf

Scroll to bottom of file, add the following

[USBDrive]
comment=USB Drive Share
path=/mnt/usbdrive
browseable=Yes
writeable=Yes
only guest=no
create mask=0777
directory mask=0777
public=no