Setting up my own blockchain

Hello to all,

i would like to set up my own Proof of Stake blockchain. I found a tutorial here

The repository is this:

The problem what i have is with following instructions:

So my questions are:
I downloaded Github to my computer and the repository is also through github available. But when i go to the folder i dont find “npm install”. Where is it? Or is it a command line, but where should i execute it? I have no idea

thanks in advance