I have searched online for ages to change my mod .zip files to .package but I can't find a single site that has .package included. Does anyone know of any? I'm on a Mac if it involves downloads.
Or does anyone know any other extension I change .zip files to in order for them to work in the game? Maybe post a link as well?

.Zip files are archive files, meaning they group the files together. The game doesn't read .zip files (except script mods, which shouldn't be unzipped)

You should be able to double-click on the .zip files to unzip them.

The exception to above advice is if you have downloaded a modding tool like s4pe. In that case you will have to obtain the proper unzipper, 7zip, and fully extract it using that.

If you're on a Mac, as the OP states, then you can't just double-click a .zip file to unpack it like you can do on a PC (unless that ability has been added to OS X since Snow Leopard, which is what my old Mac runs on). To unzip .zip (and .rar) files on a Mac, you need to download a utility that does that. I use The Unarchiver: http://unarchiver.c3.cx/unarchiver . It's freeware.

Apple used to include a program called StuffIt Expander to decompress zipped files. So if you have a older version, be sure to check for it. If you have a newer version, you can go here to download a free version of it.
I have no idea why they'd get rid of it.