During the boot sequence, it will ask for manual input, but you can skip these steps.

Once you are prompted to log in, take note of the port numbering of your system.

You can get the numbering by taking the ethernet port from a nearby computer and testing each port. (If you can, physically label these ports)

When prompted to log in, do so by using installer as the username and opnsense as the password.

When the device reboots remove the USB, otherwise you will reboot back into the installer.