mkpkg
mkpkg is not a standard Linux command. You may be thinking of tools like makepkg (Arch Linux package builder), dpkg-buildpackage (Debian), or rpmbuild (RPM-based systems) that create binary packages from source.
mkpkg is not an official Linux utility. If you encountered this term, it likely refers to a custom script or a misremembering of actual package-building commands used across different Linux distributions.
Common package builders include: makepkg (Arch Linux), dpkg-buildpackage (Debian/Ubuntu), and rpmbuild (RedHat/CentOS). Each takes source code and metadata to produce installable binary packages specific to their distribution.
If you're learning package management, research your distribution's specific tool. For example, on Arch Linux you would run makepkg -si in a package directory to build and install a package from a PKGBUILD file.