This is a simple web site built using the Monaco editor and the qsharp npm package.
Build the entire repo by running ./build.py in the root directory.
If you only want to build the functionality necessary to run the playground, you can use python .\build.py --wasm --npm --play.
Then make ./playground your current directory and run npm start to start the web server.
Copy the URL that will be printed to console and open it in a browser to use the playground.