Okay, so you can put the folder whereever you want. The important thing is you should unpack the image pack, which should result in a folder called 'assets'. You want to put the html file into the folder -with- the asset pack, but not -inside- the asset folder. So your game folder, wherever you have it, should have the html file and the assets folder.
Click on the html and it should open and play automatically. If you see a bunch of ? around and no images, that means the asset folder isn't where the game is.