Have not used Lightroom classic for 5+ years, how to install catalog?

I have not used Lightroom Classic for many years. I recently got a new desktop computer and I want to use LRC again. My photo library is still intact on an external hard drive. 

I installed LRC on the new PC. My old catalogs were backed up at E\Lightroom Backups. What is the proper way to import all these photos (1.5T) and reinstall the catalog? I don’t want to lose all of the work I did in the past. 

Thanks!