Mini Micro is a downloadable program; you run it under Windows, macOS, or Linux. That's where you'll write your game (using MiniScript code). Then you'll build for the web following these instructions (with help from me if needed).
And there are a ton of demos included with Mini Micro in the /sys/demo directory. The "Getting Started" video above shows you how to get to them. If you have any questions, don't be shy — I'm on Discord and the forums most of the day, and always happy to help!