The Power Apps CLI is the command-line interface that is used to build Power Apps Component Framework controls.
To install it, go to the link https://aka.ms/PowerAppsCLI which will download the PCF file. Click to open the powerapps-cli-1.0.msi file:
If we go into Windows Add/Remove Programs, we can see the Microsoft PowerApps CLI has been installed:
If we go to a Command Prompt and type pac, we see the CLI has been installed:
And typing pac install latest will update it to the latest version: