If you asking yourself why this app is not available through the Mac App Store the answer is: Apple stopped accepting apps that use synthetic events (simulated user input) in 2014.
You can read more about this here: https://www.imore.com/mac-app-store-and-trouble-sandboxing

In order to prevent authorized access to your Mac the app uses HTTPS connection and authorization mechanism you can enable in the app settings. When enabled for every new device that tirs to connect to your Mac - authorization dialog will be presented where you will be able to choose if to allow or deny access (can be changed from the app Preferences later).

On most networks the app should be able to detect your Mac automatically.
But if you are using some kind of public network like in hotel or school, automatic connection might not be possible.
To overcome this issue you can use QR code.

If automatic discovery doesn't work, you can scan QR code with your iPhone/iPad.
Display QR code on your Mac, and use iOS app to scan it.

No Wi-Fi network or you network blocks connection to your Mac, you have couple of options: