Perhaps my 'simple' explanations-
The Lightroom system consists of-
1. The software program- installed in your computer system.
2. Your original (out of camera) image files. (NEF, CR2, etc) (You must have backups!)
3. A Catalog database file. ( catalog filename.LRCAT )
4. A "Previews" folder (like a cache) where LR creates multiple size previews for the thumbnails and zoomed screen views.
5. [Optional] A "Smart Previews" folder. (a cache of 'smaller' dng 'preview' files)
"Importing" achieves one OR two things- Import from a hard-drive (using "ADD") creates previews of images in the Catalog.
Import from a camera card ( using "COPY") both Copies the files to the hard-drive AND creates previews of images in the Catalog.
The "Catalog" file (.LRCAT) is a database file that contains everything you do in Lightroom- all your develop edits, metadata, keywords, etc. You must have frequent backups of this catalog. (done when you close LR ). The Catalog contains specific references to the exact location of your original images, so moving the images or catalog presents problems. But there are answers!
Using LR on two computers is problematic because LR is not designed to sync information between two computers.
If you want to bring images and catalog information from a laptop into a desktop, it will be by using the menu option to "Import from another Catalog"
I suggest you read up on this topic or watch a few videos-
I understand that Lightroom builds a preview of the image and then when editing the preview lightroom records the editing info in a .lrdata file.
Your edits are stored in the .LRCAT file, which is also known as the catalog file or the Lightroom catalog. They are not stored in the .LRDATA folder (which is not a file).
Is the created .lrdata file that says "preview" contain both the preview and the recorded editing info, or are there two different files?
.LRDATA is not the same as .LRCAT, these are two different things. The edits are in the .LRCAT file. In general, users do not need to worry about the .LRDATA, you can use Lightroom without ever knowing about or doing anything with the .LRDATA.
Where does lightroom save the .lrdata file by default?
Don't worry about it, you will most likely never need to know this.
When photos are imported to Lightroom does their link, preview and related info always go into a file in the open Catalog?
The link and any work your perform on the photo (edits or assigning metadata) go into the Catalog file (not a "file in the open catalog"). The previews go to the preview cache.
If so, then I am thinking all imported photo info that I have ever imported into lightroom (which would consist of numerous folders of pics over time) will be in the catalog, what is that folder called and were is it?
The catalog is NOT a folder! The catalog is a single file! If you open the Catalog Settings, you can see the exact file name. See the example of Catalog Settings at this link: http://mcpactions.com/2013/08/14/backup-lightroom-catalog/
I believe that wobertc has provided links that describe how to use Lightroom on location and then transfer the results to your main computer. Please study these carefully. Also please stop worrying about the previews, you do not need to do anything with your previews, Lightroom manages these so you don't have to. You have gotten into a level of detail that is unnecessary for this work, misunderstood some concepts, and it is preventing you from doing actual work.