How to move pictures to a folder, not copy them

No. Not really. there is actually only one repository for photos in the photos app. When you add a photo to an album, you're basically just tagging it with a label that causes it to show in a specific album. The 'folders' are virtual.

You do not have direct access to the file system in iOS as you do in an Android based device.

Apple’s Photos app allows organizing of photos and images into albums. Those are not actual folders like on a computer, though. It isn’t managed at the directory level on disk.

A new folder in Photos can contain albums (with photos), not loose photos. I.e. a ‘folder’ is a collection of one or more albums.

Organizing photos this way doesn’t copy the photo files, rather organizes them in a database-like structure. Photos in multiple albums are still one file. Any photo or image in the Photos app is also part of the Library of all photos and images.

It is probably not “like Android”, as Apple thought this would be much better for the majority of users, as in: an improvement.

They really aren't copied to a folder in iOS. They are as KiltedTim correctly suggests simply pointed to the folder. If your fear was you were storing two copies of a photo, you aren't. You only have the one photo in your photo library, which can be pointed to folders as you choose.