Note You can't (for obvious reasons) configure your network while connected to something that may disconnect (like the WiFi). Use a hard-wired connection to your controller to use this provider.
Functionality first needs to be added to the go-unifi SDK.
You can browse documentation on the Terraform provider registry.
You can use the provider via the Terraform provider registry.
You can download a pre-built binary from the releases page, these are built using goreleaser (the configuration is in the repo). You can verify the signature and my key ownership via Keybase.
If you want to build from source, you can simply use go build in the root of the repository.
To use an external provider binary with Terraform (until the provider registry is GA), you need to place the binary in a plugin location for Terraform to find it.