Pre-req

Make sure you've got Node.js installed on your workstation, than open your terminal and type the following command:

node -v  || brew install node && node -v                                                           

Install npm

brew install npm

OR USE a CodeSpace

New Codespace

Create a new App using template

• if you're using npm (the package manager bundled with Node.js):

  npx create-probot-app my-probot-app

and follow the instructions printed on the terminal as you go. create-probot-app will then take care of the heavy lifting required to setup a Probot app development environment, with proper folder structure, and even installing all the basic Probot dependencies.

Configure

Run npm start to start the server:

Open the url shown in above step in your browser and follow instructions to register your app.

This step will create .env with the following

WEBHOOK_PROXY_URL
APP_ID
PRIVATE_KEY
WEBHOOK_SECRET
GITHUB_CLIENT_ID
GITHUB_CLIENT_SECRET

Reference

Probot docs