Clash of Clans is only available for mobile devices. It can be downloaded for free either from the Google Play store or from the Apple iTunes store.
While Clash of Clans is only technically available for Android and Apple devices, it is not unheard of for people to modify their computers to support the game as well. However, by modifying their computers to support the Clash of Clans app, users are violating the Supercell Terms of Service and may have their Clash of Clans account terminated. When in doubt, use the app the way it was originally intended to be used.