Prior to installing Screens Connect, make sure that you created your Screens ID. A Screens ID is similar to an Apple ID - you create one Screens ID that you use everywhere:
To register a computer with Screens Connect
Download Screens Connect from the product page to make sure you have the right version for your particular Mac. These instructions are for Screens Connect 4, which requires macOS 10.11 or later. You'll find instructions for previous versions here.
If you are looking for instructions for Screens Connect for Windows, the user guide can be found here.
Launch the app.
It is recommended, but not mandatory, to install Screens Connect in your /Applications folder. If not installed in the recommended folder, the app will ask you to move it there on first launch. Note that when running on macOS 10.12 Sierra, due to security restrictions introduced in Sierra, Screens Connect will be unable to update itself unless it's installed in the standard /Applications folder.
The Welcome Guide appears. (The Welcome Guide is also available from your Mac’s system menu bar icon.)
Follow the instructions included in the Welcome Guide. This will ensure your Mac is configured properly.