Hello, NicoleMarie17.
Thank you for participating in the Apple Support Communities.
We understand that you’ve been attempting to install a supplemental update on your MacBook from the Mac App Store, but you’re getting an NSURLErrorDomain error code when you try.
If you’re on a later version of the macOS software, most of your supplemental updates should be available through System Preferences > Software Update. This article will explain:
How to update the software on your Mac - Apple Support
If you’re running a previous macOS or OS X version, see if you can download it directly from here:
Apple - Support - Downloads
Warmest Regards.