PS3 HEN is a homebrew environment that allows users to run unsigned code, including games, on their PlayStation 3 console. It's an alternative to CFW (Custom Firmware), which requires a more complex installation process.
To access PS3 HEN games PKG links, you'll need to have a PS3 console with HEN installed, as well as a way to transfer files to the console (e.g., a USB drive or FTP client).
PKG files are packages that contain game data, including the game itself, updates, and other related files. These files are typically used for digital distribution on the PlayStation Store, but can also be used for homebrew purposes.