Select the file(s) in your Windows Explorer or macOS Finder.
Drag and drop them onto the Mylio Photos application window.
In the Copy Files dialog:
Select the destination location.
Assign relevant categories (if desired) for the selected file(s).
Exclude suspected duplicate files is toggled ON by default.
Delete files after adding them is toggled OFF by default.
Expand Show Advanced Settings for more options.
Click Copy Now to copy the folder into your Mylio Photos Library.