Pre/During/Post install/uninstall custom scripts should be placed here.
A script Template and Mods Functions are included as example to get you started...

Scripts that are considered:
AppID-preinstall.ps1, -install.ps1, -installed-once.ps1, -installed.ps1, -preuninstall.ps1, -uninstall.ps1 or -uninstalled.ps1

If you're using WAU (Winget-AutoUpdate) they get copied to the WAU mods directory (except -installed-once.ps1 and -uninstall.ps1) and also runs when upgrading apps in WAU.

They are deleted from WAU on an uninstall (if deployed from Winget-Install)