Sorry for the late reply, I was preparing for an exam the past days. LuCI is a settings panel developed as a basic component of OpenWRT, which basically consists of a list of settings (Click to select, drop down, input box, etc. things we can normally see in the settings interface), and some information such as IP address and load statistics.
For settings part, see https://openwrt.org/docs/guide-user/base-system/uci