I imported all of my photographs into the Photos app on my Macbook Pro. Now, I have no idea how to access these photos in Lightroom in order to edit them. I didn't even have LIghtroom at the time I took some of those photos, but now I would very much like to edit them...
You use the term 'Import' implying you mean to use Lr Classic CC. Is that correct?
Use Finder to locate where on your drive the photos are stored.
I'd move them to a new folder named something like 'All photos' in my Pictures folder.
Then, from that new folder, Import them into Lr.
If your intent is to ADD them to Lr CC (cloud ecosystem) do steps 1 & 2 above then ADD them using either Lr CC for Web or for Desktop.
As always - PLEASE backup your system using either (I use both) Time Machine (or similar) and/or Manual Backup before attempting a new operation.