This is a simple step-by-step guide to install nerd fonts in Ubuntu

Downloading

Download the font you want from Nerd Fonts website
https://www.nerdfonts.com/font-downloads

Unzip the file downloaded

Replace UbuntuMono.zip with the font you just downloaded

filename=UbuntuMono.zip
extension="${filename##*.}"
filename="${filename%.*}"
mkdir ${filename} && pushd ${filename}
unzip ../${filename}.${extension}
popd

Moving to the correct location and update font cache

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.