Login to your property from the admin portal (in a browser on your computer or your phone) and go to the units page. Search for the unit. If it doesn't already exist, click the nav menu on the right. You should see a "Setup" link. Click that and it will take you to the setup application which will walk you through each step of the setup process one step at a time.
If the unit does already exist (it's just inactive) go to the unit you just installed the devices in, and then click "add devices". The unit setup interface will launch and walk you through how to setup the devices and unit.