How do you synchronize your photos on the Google Cloud?

I have been unconsciously using Google's cloud for some time. On the other hand, I have quite "oldschool" always loaded my pictures on the laptop and very old are still on an external storage space. Now I'd like to have all the photos in one pile and most of all in the Google Cloud, because it's too late anyway.

Can you help me, as I without double photos my Google photos with my photos on the PC and ext. Can sync memory card?

Just drag the photo folder into the cloud

Will the folder be copied in or really synced without duplicate photos? And then is the date correct?

It is copied in and with every device where you have logged in with the Google Account you have access to all photos and everything in the cloud.

Unfortunately, you did not understand my question, do I have countless pictures twice, or does Google recognize that a picture already exists and does not save it twice?