The instructions for the switches are referring to manual controllers like another switch, keypad, or remote control for example. Adding devices to the EZSrve is done through the web interface, not through the tapping of the set button.
You’ll want to install, at the very least, the primary switch(the one controlling the load) in your 3-way scenario into your EZSrve database for remote control of your lights.
If you want all switches in a multi-way setup to be in the same status as the primary switch, however, you’ll need to add all switches to the EZSrve database and then create a scene in which the EZSrve is the controller and all the switches in the scenario are responders.
Instead of cross-linking INSTEON switches manually, by adding all the switches to the EZSrve database, you can easily cross-link them so that all switches will control each other and they’ll all be in the same status, ON or OFF.
I hope that helps 🙂