You cannot run PKGi on a standard retail PS3. Your console must be running custom firmware (CFW) or Hybrid Firmware (HFW) with HEN (Homebrew Enabler). Here is the checklist:
No need to manually source PKG files; integrates download and installation into one interface. ps3 pkgi install
The process is simple: jailbreak your console, transfer the .pkg file, configure a database, and start downloading. While it requires 15 minutes of setup and basic troubleshooting, the payoff is massive. You cannot run PKGi on a standard retail PS3