First of all, you need to install meteor on your computer : https://www.meteor.com/install
Then you simply need to download the code or to clone the repository.
In order to run the application, you need to open the command prompt and navigate to your app folder (ex: cd c:/../MeteorFirstApp)
Before running the server, we need to install all package by writing : meteor npm install
Then just enter the following command to run the server : meteor.
Then open your browser and go to the following url : http://localhost:3000/