First, go to this link: https://2derp4you.itch.io/big-chungus-game¨

Here, you can either play the webbrowser-version (0.3) Or you can play other newer versions by downloading the game.

There are install instructions on the web-page, so just follow them and download the game.

If you have windows 10, you're gonna get a virus warning the first time you open the game. If you're not comfortable with still running the game, you can just play it in your browser, but there isn't any actual virus you can get from the game.