The gallery is a very lightweight app that doesn't give you any tools for organizing your collection of images (other than deleting or sharing images)
The above suggestions will allow you to do what you are looking to do or you could use a separate file manager. I use Astro file manager. If you create a new folder using Astro then put images into that folder the gallery will show the new folder as an album. You can also move images from one folder to another to change which album they are associated with in the gallery.
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