nerdfont.csv is a generated CSV that includes all of the Nerd Font icons and their description, as found on Nerd Font's Cheat Sheet website.
nerdfont.txt is a more readable version of that file
You will need to open the files with an editor that has a Nerd Font installed for.
A simple icon picker can be built with rofi (or dmenu) and the provided nerdfont.txt file. This picker will copy the icon to the clipboard (requires xsel installed)
cat "nerdfont.txt" | rofi -dmenu -i | awk '{print $1}' | xsel -i -b