You need to seperate your education from getting your products to work. Since http://www.google.com/search?&q=SCSI+FAQ finds documents which cover your "what is" questions.

When you sort it out to condense it down to I have this and want to use it with this OS and this application, then we can proceed. Beware that some SCSI tape drives are strictly historic dumpster bin finds and you need to just EBAY it for something that works.

Bob