feedback on failure to export images on desktop

Hello my name is Vlad!

I recently tried for the first time Adobe Lightroom and ran into a problem:

I imported a folder (with a name) from my desktop into Lightroom and once the images uploaded into the library module I made the mistake to put in the trash the folder and emptied the trash  but a couple days later when I tried to export the images back into the desktop via a folder through Lightroom I ran into some snags.  For example if I clicked on an image(s) and select them I would get a message such as "Source file(s) are online or missing. Another issue is when I want to export as Catalog all the images shown in the library module I am then asked to save as (to create a new name for the folder) and hit Export however I get a message telling me Lightroom was able to successfully export some of the photos to the new catalog but encountered these problems: "Photos could not be found" showing the list of the titled images.  Last but not least is when I look under Folders I see the name of the original folder that I had imported initially into Lightroom showing all the images displayed in the library module and I am told that this folder contains 50 images and if I want to remove the folder the photos will be removed from the Lightroomcatalog but the folder and files will remain on disk.  But what is the disk?  The hard drive or a disk?  I'd appreciate some feedback.  Thank you very much!