I will assume that when you attach the usb drive it appears in /dev as a new SCSI device (e.g. /dev/sda). In that case then a standard "mount /dev/sda1 /mnt/usb" will do the trick. If the drive doesn't appear in /dev then use "modprobe usb-storage" to load the usb mass storage protocol module which most usb drives use. (Both mount and modprobe require superuser privelages)
If this doesn't work then it is possible that your usb disk uses its own proprietry protocol in which case the only option is to check whether the vendor supplies a driver or whether someone has already written one. If searching doesn't find anything then I'm afraid your usb drive won't work at the moment although you should still keep an eye open as one may be developed in the future.
The likelihood is very high that the drive you are using does work with the usb-storage module (all that I've ever tried do) and hopefully this should prove relatively painless