Example can be found at examples. The following is a simple step-to-step instruction for rp2040. For other microcontrollers, the steps should be identical with a debug probe.
If you have a debug probe connected to your rp2040 board, flashing is quite simple: run the following command to automatically compile and flash RMK firmware to the board:
If you don't have a debug probe, you can use elf2uf2-rs to flash your rp2040 firmware via USB. There are several additional steps you have to do: