Please see Klipper Architecture / Ecosystem for a general understanding of the Klipper system.
No. The so-called “host”, i.e. the computer that runs Linux and where you have installed Klipper naturally has no USB ID.
See RPi microcontroller - Klipper documentation how you could use this computer as an additional “soft MCU”. Usually rarely needed
Every hardware that has an own microcontroller (STM32xxx, RP2040 etc) and is either connected via USB, CAN or UART to the above-mentioned host needs to have some [mcu] statement in the config so that Klipper knows to whom to talk to.
The “primary” board (where the bed is connected and most of the stepper drivers sit) is typically the [mcu] and the other boards (tool boards, eddy sensors etc) need to have a unique name like [mcu eddy] or similar. This name is also then used to address functions of this hardware.
You need to check the relevant documentation of the individual pieces, e.g. GitHub - bigtreetech/Eddy for their correct configuration.
Typically, Voron has a quite good documentation, so it might be worthwhile to read it in addition.