External Hard Drive import to Lightroom

[defaultnkow6khkxuzl]

I imported from an external hard drive to a catalog in Lightroom. Now it says File cannot be found. 

I am using a MacBook.
The images were saved onto the hard drive from an HP. 
What did I do wrong? Can it be fixed without having to re-download? 

[Peru Bob]

I've moved this from the Using the Community forum (which is the forum for issues using the forums) to the Lightroom forum so that proper help can be offered.

[JP Hess]

When you import images to a Lightroom catalog, the images are added and are referenced in the catalog which is a database. However, the images are not physically added to the catalog. They are left in their folders so they should still be on that external hard drive. Can you use Finder and still see those images in their folder on the external hard drive?