I have photos and videos on another device that I’d like to copy to my phone. Which folders on my phone should I copy these to if I want these to be visible in Gallery?

Copy the photos to the Images folder in the phone’s mass memory root, or if you have a memory card in use, to the Images folder in the memory card root.

Similarly, copy the videos to the corresponding Videos folder.

Do not copy any photos or videos to the DCIM folder in the mass memory. Your phone uses the DCIM folder for photos and videos that are captured with the phone.