How to use iPhone extra battery case?

I bought an EC technology external battery case and there wasn't any instructions on how to use it.

Do I allow it to charge my phone and then recharge after it's empty?

I typically charge my phone overnight… Do I turn the case on to allow it yo charge and keep the case plugged in also?

So confused! Thanks for any helps, tutorials, or videos to help

Not familiar with this battery case, but by what you've said here I can only imagine it's simply "plug & play" just connect to your phone and charge as if you haven't added anything, your iPhone battery will still have to top off first or both act as one and charge together, usually there's one button at least in the extra battery case, this lets you keep the extra one full until needed, but will have to be left in the "on" position to charge. If there's no switch then both batteries will act as one, and possibly show as one. With it off (the battery case) check your usage and times, then plugged in those same times should be vastly longer in all catogories.