Your hardware must be initially provisioned with the Toit firmware, before you can benefit from the Toit platform and all the features available.
Provisioning means that the hardware is being granted a unique hardware ID used for the remaining of its lifecycle, and the latest released Toit firmware will be installed on the hardware.
Your WiFi credentials are added in the provisioning step, letting your ESP32 get online and accessible from the Toit console. Additional connection settings can be added later on.
Note that your computer does not need to be on the same WiFi network as your ESP32 in order to get your ESP32 online during initial provisioning.
Provision your hardware using the Web Serial interface and follow the steps in the guide.
When the ESP32 has been initially provisioned with WiFi credentials, the ESP32 device is connecting to the network via WiFi. The serial connection is purely for debugging the device if WiFi connection is lost. In other words, you can plug the ESP32 into another power source and communicate with the ESP32 over WiFi from now on. Later on you can always add other connection types, like cellular connection.