Copy/pasta from my guide (noteworthy parts bolded):
Once [dropbox is] installed, you should have somewhere on your computer a ‘dropbox folder’. Simply copy the entire web folder to the dropbox folder (you can rename the web folder if you want to keep your dropbox looking neat). From there, find one of the index files, and select ‘share link’. Dropbox should give you a link that you can post to allow people to play your game. If the link takes you to a page with a button to download the game, make sure the link you have starts with dl. and not www. (If it does start with www., you can simply change it to dl., which should allow people to play your game without downloading it.)