posdibly off topic, but don’t confuse them with .pkg.tar.zst, which are actually arch packages that can be installed with pacman -U .pkg.tar.zst . You’ll most likely know them from installing manually from the AUR.

You don’t, a tar.gz is an archive format like zip or 7z

Technically it’s two formats a tarball - all files combined into one file, tar - and then compressed into a gzip.

To uncompress and release the files run:

tar -xzf filename.tar.gz

More info here: https://www.howtogeek.com/362203/what-is-a-tar.gz-file-and-how-do-i-open-it/