Don't know your case, but some general info:
If your case has 2 external scsi connectors, you can remove the jumper for termination on the drive and use an external terminator (something like a thick connector). Or plug it in the chain before the terminator. Otherwise, put the jumper for termination and your drive and the end of the chain.
Now, there will be a push-button up-down switch at the back to set the scsi-id. On the inside, there will be a lot of cables coming out of it ending in connctors fitting on the jumpers of your drive. Normally, one is black and is the common and need to go make contact on the bottom row of the pins where you put the jumpers. The others need to be set at the top row of the jumpers used to set the scsi-id. If they are not labelled (or in the manual), it is a trial and error thing. You will also find a flatcable and power connector but these are simple.
Now, connect to the pc and terminate the unused conector. Set a scsi-id that is not yet used on the pc. When starting, go to the bios of the scsi controller and set it to activate the external connector. It can be that is always active, or that you have to set it, also check for options regarding termination. You will also be able then to check if the id you chose is ok.
If that is ok, reboot and the drive should be there.
PS: alwasy turn on the extrenal drive before turning on the pc. If you wait to long, it can be that the controller found nothing and turned of the external chain.
Check out
http://www.paralan.com/artech1.html for all the information possible about scsi.