I don't understand how to have my files on MacBook Air, iPad Air and iPhone 8 sync?

I have a MacBook Air with latest OS, an iPad Air 6th Gen-2018 and and iPhone 8 256gb. I'd like to be able to sync the Files App with all 3 for use in my business to have access to info in Files from any device. I understand how to sync using iCloud but would rather have all the info stored on each device memory when wifi is unavailable.