Relational / Lookup Fields

I've read through all of the FAQs / forum postings and watched every video I could find. I'm STILL completely lost when it comes to linking tables together. So, please, if the answer comes in the form of "follow these instructions," please don't bother. How about, instead, a couple of real world examples that I can copy into my database for review?

Here's what I'm trying to accomplish.

Our customers can purchase 3 TYPES of pre-paid instruments. Each table contains a column with the exact same name.

I want to create a report / table / flying monkey (I don't care what it's called) that will link those three tables together and show, on a client by client basis, whatever pre-paid instrument information we have on file.

Every time I go to create something, not only do I get errors no matter what steps I take, all with terms like NULL values and the like, I get more frustrated. The way to handle errors basically -- to me -- say, "If we encounter an error, we'll start deleting records or set the value to zero. Which would you prefer?" How about *neither*? How about an easy way to link up three tables with a common data element, and produce a one-to-many relational report?

And while we're on the subject: Once it's been figured out how to associate all of these tables. (BTW, why isn't there a "copy table" function so I can make a backup of a table before I probably destroy it?) Once the linking is figured out, there HAS to be some way to FILTER a report so that my admin staff can look up a SINGLE client and not have to wade through hundreds of them.

Thanks to anyone who can provide some answers.