To configure Wi-Fi using the Particle CLI, use the following command from a Terminal or Command Prompt window:

particle serial wifi

This will interactively prompt you for the information needed to connect to your Wi-Fi network. The device must be in listening mode (blinking dark blue) for this command to work.

Upon successful completion, the device should be breathing cyan (light blue).

The Particle CLI command reference includes more information about this and other comamnds.