It's probably best explained in a video on what may be the best youtube channel on OpenWrt-related things: https://www.youtube.com/watch?v=FFTPA6GkJjg
Or, if you prefer textual information: https://openwrt.org/docs/guide-user/installation/attended.sy... (OpenWrt's infra is kinda slow today for me, must be many people checking out the new release :))