This is a simple step-by-step guide to install nerd fonts in Ubuntu
Download the font you want from Nerd Fonts website https://www.nerdfonts.com/font-downloads
Replace UbuntuMono.zip with the font you just downloaded
filename=UbuntuMono.zip
extension="${filename##*.}"
filename="${filename%.*}"
mkdir ${filename} && pushd ${filename}
unzip ../${filename}.${extension}
popd
Now, let's create a .fonts directory and move the new font there
mkdir -p ~/.fonts
mv ${filename} ~/.fonts/
Last, but not least, we need to update Ubuntu's font cache
fc-cache -fv
You should now be able to see have the font available.